Add "P" parameter to M302

Marlin/Marlin_main.cpp

 #if ENABLED(PREVENT_DANGEROUS_EXTRUDE)
 
   /**
-   * M302: Allow cold extrudes, or set the minimum extrude S<temperature>.
+   * M302: Allow cold extrudes, or set the minimum extrude temperature
+   *
+   *       S<temperature> sets the minimum extrude temperature
+   *       P<bool> enables (1) or disables (0) cold extrusion
+   *
+   *  Examples:
+   *
+   *       M302         ; report current cold extrusion state
+   *       M302 P0      ; enable cold extrusion checking
+   *       M302 P1      ; disables cold extrusion checking
+   *       M302 S0      ; always allow extrusion (disables checking)
+   *       M302 S170    ; only allow extrusion above 170
+   *       M302 S170 P1 ; set min extrude temp to 170 but leave disabled
    */
   inline void gcode_M302() {
-    thermalManager.extrude_min_temp = code_seen('S') ? code_value_temp_abs() : 0;
+    bool seen_S = code_seen('S');
+    if (seen_S) {
+      thermalManager.extrude_min_temp = code_value_temp_abs();
+      thermalManager.allow_cold_extrude = (thermalManager.extrude_min_temp == 0);
+    }
+
+    if (code_seen('P'))
+      thermalManager.allow_cold_extrude = (thermalManager.extrude_min_temp == 0) || code_value_bool();
+    else if (!seen_S) {
+      // Report current state
+      SERIAL_ECHO_START;
+      SERIAL_ECHOPAIR("Cold extrudes are ", (thermalManager.allow_cold_extrude ? "en" : "dis"));
+      SERIAL_ECHOPAIR("abled (min temp ", int(thermalManager.extrude_min_temp + 0.5));
+      SERIAL_ECHOLNPGM("C)");
+    }
   }
 
 #endif // PREVENT_DANGEROUS_EXTRUDE

Marlin/temperature.cpp

 #endif
 
 #if ENABLED(PREVENT_DANGEROUS_EXTRUDE)
+  bool Temperature::allow_cold_extrude = false;
   float Temperature::extrude_min_temp = EXTRUDE_MINTEMP;
 #endif
 

Marlin/temperature.h

     #endif
 
     #if ENABLED(PREVENT_DANGEROUS_EXTRUDE)
+      static bool allow_cold_extrude;
       static float extrude_min_temp;
       static bool tooColdToExtrude(uint8_t e) {
         #if HOTENDS == 1
           UNUSED(e);
         #endif
-        return degHotend(HOTEND_INDEX) < extrude_min_temp;
+        return allow_cold_extrude ? false : degHotend(HOTEND_INDEX) < extrude_min_temp;
       }
     #else
       static bool tooColdToExtrude(uint8_t e) { UNUSED(e); return false; }