Send notifications to ExtUI for M0/M1 (#13344)

- Send notifications to ExtUI for M0/M1

- wait_for_user can be non-volatile (not changed by interrupt)
  C / C++ compilers don't optimize away reads of non-volatile variables when a function call is used between accesses, because *any* variable could be changed by the function call. Since `wait_for_user` can't be changed without a function call, it should be non-volatile so the compiler can optimize away cases where it is read more than once without an intervening function call.

Marlin/src/Marlin.cpp

 
 // For M0/M1, this flag may be cleared (by M108) to exit the wait-for-user loop
 #if HAS_RESUME_CONTINUE
-  volatile bool wait_for_user; // = false;
+  bool wait_for_user; // = false;
 #endif
 
 #if HAS_AUTO_REPORTING || ENABLED(HOST_KEEPALIVE_FEATURE)

Marlin/src/Marlin.h

 extern volatile bool wait_for_heatup;
 
 #if HAS_RESUME_CONTINUE
-  extern volatile bool wait_for_user;
+  extern bool wait_for_user;
 #endif
 
 #if HAS_AUTO_REPORTING || ENABLED(HOST_KEEPALIVE_FEATURE)

Marlin/src/gcode/lcd/M0_M1.cpp

   #include "../../lcd/ultralcd.h"
 #endif
 
+#if ENABLED(EXTENSIBLE_UI)
+  #include "../../lcd/extensible_ui/ui_api.h"
+#endif
+
 #include "../../sd/cardreader.h"
 
 #if HAS_LEDS_OFF_FLAG
       #endif
     }
 
+  #elif ENABLED(EXTENSIBLE_UI)
+
+    ExtUI::onUserConfirmRequired(has_message ? args : MSG_USERWAIT); // SRAM string
+
   #else
 
     if (has_message) {
   else
     while (wait_for_user) idle();
 
+  #if ENABLED(EXTENSIBLE_UI)
+    ExtUI::onUserConfirmRequired(nullptr);
+  #endif
+
   #if HAS_LEDS_OFF_FLAG
     printerEventLEDs.onResumeAfterWait();
   #endif

Marlin/src/lcd/extensible_ui/lib/example.cpp

      */
   }
   void onIdle() {}
-  void onPrinterKilled(const char* msg) {}
+  void onPrinterKilled(PGM_P const msg) {}
   void onMediaInserted() {};
   void onMediaError() {};
   void onMediaRemoved() {};
   void onPrintTimerPaused() {}
   void onPrintTimerStopped() {}
   void onFilamentRunout() {}
+  void onUserConfirmRequired(const char * const msg) {}
   void onStatusChanged(const char * const msg) {}
   void onFactoryReset() {}
   void onLoadSettings() {}

Marlin/src/lcd/extensible_ui/ui_api.cpp

     feedrate_percentage = clamp(value, 10, 500);
   }
 
+  void setUserConfirmed(void) {
+    #if HAS_RESUME_CONTINUE
+      wait_for_user = false;
+    #endif
+  }
+
   void printFile(const char *filename) {
     IFSD(card.openAndPrintFile(filename), NOOP);
   }

Marlin/src/lcd/extensible_ui/ui_api.h

   void setRetractAcceleration_mm_s2(const float);
   void setTravelAcceleration_mm_s2(const float);
   void setFeedrate_percent(const float);
+  void setUserConfirmed(void);
 
   #if ENABLED(LIN_ADVANCE)
     float getLinearAdvance_mm_mm_s(const extruder_t);
   void onMediaError();
   void onMediaRemoved();
   void onPlayTone(const uint16_t frequency, const uint16_t duration);
-  void onPrinterKilled(const char* msg);
+  void onPrinterKilled(PGM_P const msg);
   void onPrintTimerStarted();
   void onPrintTimerPaused();
   void onPrintTimerStopped();
   void onFilamentRunout(const extruder_t extruder);
+  void onUserConfirmRequired(const char * const msg);
   void onStatusChanged(const char * const msg);
   void onFactoryReset();
   void onStoreSettings();