Add "Marlin Dev Mode" option

Marlin/Configuration_adv.h

   #define WIFI_PWD  "Wifi Password"
 #endif
 
+// Enable Marlin dev mode which adds some special commands
+//#define MARLIN_DEV_MODE
+
 #endif // CONFIGURATION_ADV_H

Marlin/src/config/default/Configuration_adv.h

   #define WIFI_PWD  "Wifi Password"
 #endif
 
+// Enable Marlin dev mode which adds some special commands
+//#define MARLIN_DEV_MODE
+
 #endif // CONFIGURATION_ADV_H

Marlin/src/config/examples/AlephObjects/TAZ4/Configuration_adv.h

   #define WIFI_PWD  "Wifi Password"
 #endif
 
+// Enable Marlin dev mode which adds some special commands
+//#define MARLIN_DEV_MODE
+
 #endif // CONFIGURATION_ADV_H

Marlin/src/config/examples/Anet/A6/Configuration_adv.h

   #define WIFI_PWD  "Wifi Password"
 #endif
 
+// Enable Marlin dev mode which adds some special commands
+//#define MARLIN_DEV_MODE
+
 #endif // CONFIGURATION_ADV_H

Marlin/src/config/examples/Anet/A8/Configuration_adv.h

   #define WIFI_PWD  "Wifi Password"
 #endif
 
+// Enable Marlin dev mode which adds some special commands
+//#define MARLIN_DEV_MODE
+
 #endif // CONFIGURATION_ADV_H

Marlin/src/config/examples/Azteeg/X5GT/Configuration_adv.h

   #define WIFI_PWD  "Wifi Password"
 #endif
 
+// Enable Marlin dev mode which adds some special commands
+//#define MARLIN_DEV_MODE
+
 #endif // CONFIGURATION_ADV_H

Marlin/src/config/examples/BIBO/TouchX/cyclops/Configuration_adv.h

   #define WIFI_PWD  "Wifi Password"
 #endif
 
+// Enable Marlin dev mode which adds some special commands
+//#define MARLIN_DEV_MODE
+
 #endif // CONFIGURATION_ADV_H

Marlin/src/config/examples/BIBO/TouchX/default/Configuration_adv.h

   #define WIFI_PWD  "Wifi Password"
 #endif
 
+// Enable Marlin dev mode which adds some special commands
+//#define MARLIN_DEV_MODE
+
 #endif // CONFIGURATION_ADV_H

Marlin/src/config/examples/BQ/Hephestos/Configuration_adv.h

   #define WIFI_PWD  "Wifi Password"
 #endif
 
+// Enable Marlin dev mode which adds some special commands
+//#define MARLIN_DEV_MODE
+
 #endif // CONFIGURATION_ADV_H

Marlin/src/config/examples/BQ/Hephestos_2/Configuration_adv.h

   #define WIFI_PWD  "Wifi Password"
 #endif
 
+// Enable Marlin dev mode which adds some special commands
+//#define MARLIN_DEV_MODE
+
 #endif // CONFIGURATION_ADV_H

Marlin/src/config/examples/BQ/WITBOX/Configuration_adv.h

   #define WIFI_PWD  "Wifi Password"
 #endif
 
+// Enable Marlin dev mode which adds some special commands
+//#define MARLIN_DEV_MODE
+
 #endif // CONFIGURATION_ADV_H

Marlin/src/config/examples/Cartesio/Configuration_adv.h

   #define WIFI_PWD  "Wifi Password"
 #endif
 
+// Enable Marlin dev mode which adds some special commands
+//#define MARLIN_DEV_MODE
+
 #endif // CONFIGURATION_ADV_H

Marlin/src/config/examples/Creality/CR-10/Configuration_adv.h

   #define WIFI_PWD  "Wifi Password"
 #endif
 
+// Enable Marlin dev mode which adds some special commands
+//#define MARLIN_DEV_MODE
+
 #endif // CONFIGURATION_ADV_H

Marlin/src/config/examples/Creality/CR-10S/Configuration_adv.h

   #define WIFI_PWD  "Wifi Password"
 #endif
 
+// Enable Marlin dev mode which adds some special commands
+//#define MARLIN_DEV_MODE
+
 #endif // CONFIGURATION_ADV_H

Marlin/src/config/examples/Creality/CR-10mini/Configuration_adv.h

   #define WIFI_PWD  "Wifi Password"
 #endif
 
+// Enable Marlin dev mode which adds some special commands
+//#define MARLIN_DEV_MODE
+
 #endif // CONFIGURATION_ADV_H

Marlin/src/config/examples/Creality/CR-8/Configuration_adv.h

   #define WIFI_PWD  "Wifi Password"
 #endif
 
+// Enable Marlin dev mode which adds some special commands
+//#define MARLIN_DEV_MODE
+
 #endif // CONFIGURATION_ADV_H

Marlin/src/config/examples/Creality/Ender-2/Configuration_adv.h

   #define WIFI_PWD  "Wifi Password"
 #endif
 
+// Enable Marlin dev mode which adds some special commands
+//#define MARLIN_DEV_MODE
+
 #endif // CONFIGURATION_ADV_H

Marlin/src/config/examples/Creality/Ender-3/Configuration_adv.h

   #define WIFI_PWD  "Wifi Password"
 #endif
 
+// Enable Marlin dev mode which adds some special commands
+//#define MARLIN_DEV_MODE
+
 #endif // CONFIGURATION_ADV_H

Marlin/src/config/examples/Creality/Ender-4/Configuration_adv.h

   #define WIFI_PWD  "Wifi Password"
 #endif
 
+// Enable Marlin dev mode which adds some special commands
+//#define MARLIN_DEV_MODE
+
 #endif // CONFIGURATION_ADV_H

Marlin/src/config/examples/Felix/Configuration_adv.h

   #define WIFI_PWD  "Wifi Password"
 #endif
 
+// Enable Marlin dev mode which adds some special commands
+//#define MARLIN_DEV_MODE
+
 #endif // CONFIGURATION_ADV_H

Marlin/src/config/examples/FolgerTech/i3-2020/Configuration_adv.h

   #define WIFI_PWD  "Wifi Password"
 #endif
 
+// Enable Marlin dev mode which adds some special commands
+//#define MARLIN_DEV_MODE
+
 #endif // CONFIGURATION_ADV_H

Marlin/src/config/examples/Geeetech/Prusa i3 Pro C/Configuration_adv.h

   #define WIFI_PWD  "Wifi Password"
 #endif
 
+// Enable Marlin dev mode which adds some special commands
+//#define MARLIN_DEV_MODE
+
 #endif // CONFIGURATION_ADV_H

Marlin/src/config/examples/Geeetech/Prusa i3 Pro W/Configuration_adv.h

   #define WIFI_PWD  "Wifi Password"
 #endif
 
+// Enable Marlin dev mode which adds some special commands
+//#define MARLIN_DEV_MODE
+
 #endif // CONFIGURATION_ADV_H

Marlin/src/config/examples/Infitary/i3-M508/Configuration_adv.h

   #define WIFI_PWD  "Wifi Password"
 #endif
 
+// Enable Marlin dev mode which adds some special commands
+//#define MARLIN_DEV_MODE
+
 #endif // CONFIGURATION_ADV_H

Marlin/src/config/examples/JGAurora/A5/Configuration_adv.h

   #define WIFI_PWD  "Wifi Password"
 #endif
 
+// Enable Marlin dev mode which adds some special commands
+//#define MARLIN_DEV_MODE
+
 #endif // CONFIGURATION_ADV_H

Marlin/src/config/examples/MakerParts/Configuration_adv.h

   #define WIFI_PWD  "Wifi Password"
 #endif
 
+// Enable Marlin dev mode which adds some special commands
+//#define MARLIN_DEV_MODE
+
 #endif // CONFIGURATION_ADV_H

Marlin/src/config/examples/Malyan/M150/Configuration_adv.h

   #define WIFI_PWD  "Wifi Password"
 #endif
 
+// Enable Marlin dev mode which adds some special commands
+//#define MARLIN_DEV_MODE
+
 #endif // CONFIGURATION_ADV_H

Marlin/src/config/examples/Malyan/M200/Configuration_adv.h

   #define WIFI_PWD  "Wifi Password"
 #endif
 
+// Enable Marlin dev mode which adds some special commands
+//#define MARLIN_DEV_MODE
+
 #endif // CONFIGURATION_ADV_H

Marlin/src/config/examples/Micromake/C1/enhanced/Configuration_adv.h

   #define WIFI_PWD  "Wifi Password"
 #endif
 
+// Enable Marlin dev mode which adds some special commands
+//#define MARLIN_DEV_MODE
+
 #endif // CONFIGURATION_ADV_H

Marlin/src/config/examples/Mks/Sbase/Configuration_adv.h

   #define WIFI_PWD  "Wifi Password"
 #endif
 
+// Enable Marlin dev mode which adds some special commands
+//#define MARLIN_DEV_MODE
+
 #endif // CONFIGURATION_ADV_H

Marlin/src/config/examples/RigidBot/Configuration_adv.h

   #define WIFI_PWD  "Wifi Password"
 #endif
 
+// Enable Marlin dev mode which adds some special commands
+//#define MARLIN_DEV_MODE
+
 #endif // CONFIGURATION_ADV_H

Marlin/src/config/examples/SCARA/Configuration_adv.h

   #define WIFI_PWD  "Wifi Password"
 #endif
 
+// Enable Marlin dev mode which adds some special commands
+//#define MARLIN_DEV_MODE
+
 #endif // CONFIGURATION_ADV_H

Marlin/src/config/examples/Sanguinololu/Configuration_adv.h

   #define WIFI_PWD  "Wifi Password"
 #endif
 
+// Enable Marlin dev mode which adds some special commands
+//#define MARLIN_DEV_MODE
+
 #endif // CONFIGURATION_ADV_H

Marlin/src/config/examples/TheBorg/Configuration_adv.h

   #define WIFI_PWD  "Wifi Password"
 #endif
 
+// Enable Marlin dev mode which adds some special commands
+//#define MARLIN_DEV_MODE
+
 #endif // CONFIGURATION_ADV_H

Marlin/src/config/examples/TinyBoy2/Configuration_adv.h

   #define WIFI_PWD  "Wifi Password"
 #endif
 
+// Enable Marlin dev mode which adds some special commands
+//#define MARLIN_DEV_MODE
+
 #endif // CONFIGURATION_ADV_H

Marlin/src/config/examples/UltiMachine/Archim2/Configuration_adv.h

   #define WIFI_PWD  "Wifi Password"
 #endif
 
+// Enable Marlin dev mode which adds some special commands
+//#define MARLIN_DEV_MODE
+
 #endif // CONFIGURATION_ADV_H

Marlin/src/config/examples/Velleman/K8200/Configuration_adv.h

   #define WIFI_PWD  "Wifi Password"
 #endif
 
+// Enable Marlin dev mode which adds some special commands
+//#define MARLIN_DEV_MODE
+
 #endif // CONFIGURATION_ADV_H

Marlin/src/config/examples/Velleman/K8400/Configuration_adv.h

   #define WIFI_PWD  "Wifi Password"
 #endif
 
+// Enable Marlin dev mode which adds some special commands
+//#define MARLIN_DEV_MODE
+
 #endif // CONFIGURATION_ADV_H

Marlin/src/config/examples/Wanhao/Duplicator 6/Configuration_adv.h

   #define WIFI_PWD  "Wifi Password"
 #endif
 
+// Enable Marlin dev mode which adds some special commands
+//#define MARLIN_DEV_MODE
+
 #endif // CONFIGURATION_ADV_H

Marlin/src/config/examples/delta/FLSUN/auto_calibrate/Configuration_adv.h

   #define WIFI_PWD  "Wifi Password"
 #endif
 
+// Enable Marlin dev mode which adds some special commands
+//#define MARLIN_DEV_MODE
+
 #endif // CONFIGURATION_ADV_H

Marlin/src/config/examples/delta/FLSUN/kossel/Configuration_adv.h

   #define WIFI_PWD  "Wifi Password"
 #endif
 
+// Enable Marlin dev mode which adds some special commands
+//#define MARLIN_DEV_MODE
+
 #endif // CONFIGURATION_ADV_H

Marlin/src/config/examples/delta/FLSUN/kossel_mini/Configuration_adv.h

   #define WIFI_PWD  "Wifi Password"
 #endif
 
+// Enable Marlin dev mode which adds some special commands
+//#define MARLIN_DEV_MODE
+
 #endif // CONFIGURATION_ADV_H

Marlin/src/config/examples/delta/generic/Configuration_adv.h

   #define WIFI_PWD  "Wifi Password"
 #endif
 
+// Enable Marlin dev mode which adds some special commands
+//#define MARLIN_DEV_MODE
+
 #endif // CONFIGURATION_ADV_H

Marlin/src/config/examples/delta/kossel_mini/Configuration_adv.h

   #define WIFI_PWD  "Wifi Password"
 #endif
 
+// Enable Marlin dev mode which adds some special commands
+//#define MARLIN_DEV_MODE
+
 #endif // CONFIGURATION_ADV_H

Marlin/src/config/examples/delta/kossel_pro/Configuration_adv.h

   #define WIFI_PWD  "Wifi Password"
 #endif
 
+// Enable Marlin dev mode which adds some special commands
+//#define MARLIN_DEV_MODE
+
 #endif // CONFIGURATION_ADV_H

Marlin/src/config/examples/delta/kossel_xl/Configuration_adv.h

   #define WIFI_PWD  "Wifi Password"
 #endif
 
+// Enable Marlin dev mode which adds some special commands
+//#define MARLIN_DEV_MODE
+
 #endif // CONFIGURATION_ADV_H

Marlin/src/config/examples/gCreate/gMax1.5+/Configuration_adv.h

   #define WIFI_PWD  "Wifi Password"
 #endif
 
+// Enable Marlin dev mode which adds some special commands
+//#define MARLIN_DEV_MODE
+
 #endif // CONFIGURATION_ADV_H

Marlin/src/config/examples/makibox/Configuration_adv.h

   #define WIFI_PWD  "Wifi Password"
 #endif
 
+// Enable Marlin dev mode which adds some special commands
+//#define MARLIN_DEV_MODE
+
 #endif // CONFIGURATION_ADV_H

Marlin/src/config/examples/tvrrug/Round2/Configuration_adv.h

   #define WIFI_PWD  "Wifi Password"
 #endif
 
+// Enable Marlin dev mode which adds some special commands
+//#define MARLIN_DEV_MODE
+
 #endif // CONFIGURATION_ADV_H

Marlin/src/config/examples/wt150/Configuration_adv.h

   #define WIFI_PWD  "Wifi Password"
 #endif
 
+// Enable Marlin dev mode which adds some special commands
+//#define MARLIN_DEV_MODE
+
 #endif // CONFIGURATION_ADV_H

Marlin/src/gcode/calibrate/G28.cpp

     }
   #endif
 
+  #if ENABLED(MARLIN_DEV_MODE)
+    if (parser.seen('S')) {
+      LOOP_XYZ(a) set_axis_is_at_home((AxisEnum)a);
+      SYNC_PLAN_POSITION_KINEMATIC();
+      SERIAL_ECHOLNPGM("Simulated Homing");
+      report_current_position();
+      #if ENABLED(DEBUG_LEVELING_FEATURE)
+        if (DEBUGGING(LEVELING)) SERIAL_ECHOLNPGM("<<< G28");
+      #endif
+      return;
+    }
+  #endif
+
   if (all_axes_known() && parser.boolval('O')) { // home only if needed
     #if ENABLED(DEBUG_LEVELING_FEATURE)
       if (DEBUGGING(LEVELING)) {