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/lcd/extensible_ui/lib/example.cpp

@@ -46,7 +46,7 @@ namespace ExtUI {
      */
   }
   void onIdle() {}
-  void onPrinterKilled(const char* msg) {}
+  void onPrinterKilled(PGM_P const msg) {}
   void onMediaInserted() {};
   void onMediaError() {};
   void onMediaRemoved() {};
@@ -55,6 +55,7 @@ namespace ExtUI {
   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

@@ -630,6 +630,12 @@ namespace ExtUI {
     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

@@ -117,6 +117,7 @@ namespace ExtUI {
   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);
@@ -239,11 +240,12 @@ namespace ExtUI {
   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();