UBL Manual Build Menu Option (#6972)

One click option to manually build UBL mesh.

Marlin/language_en.h

   #ifndef MSG_UBL_LEVEL_BED
     #define MSG_UBL_LEVEL_BED                 _UxGT("Unified Bed Leveling")
   #endif
+  #ifndef MSG_UBL_MANUAL_MESH
+    #define MSG_UBL_MANUAL_MESH               _UxGT("Manually Build Mesh")
+  #endif
   #ifndef MSG_UBL_ACTIVATE_MESH
     #define MSG_UBL_ACTIVATE_MESH             _UxGT("Activate UBL")
   #endif

Marlin/ultralcd.cpp

      *
      *  Prepare
      * - Unified Bed Leveling
+     *   - Manually Build Mesh
      *   - Activate UBL
      *   - Deactivate UBL
      *   - Mesh Storage
     void _lcd_ubl_level_bed() {
       START_MENU();
       MENU_BACK(MSG_PREPARE);
+      MENU_ITEM(gcode, MSG_UBL_MANUAL_MESH, PSTR("G29 I999\nG29 P2 B T0"));
       MENU_ITEM(gcode, MSG_UBL_ACTIVATE_MESH, PSTR("G29 A"));
       MENU_ITEM(gcode, MSG_UBL_DEACTIVATE_MESH, PSTR("G29 D"));
       MENU_ITEM(submenu, MSG_UBL_STORAGE_MESH_MENU, _lcd_ubl_storage_mesh);