Add new events and accompanying logic to notify when the app is paused and resumed on Android devices.

core/os/main_loop.h

@@ -60,6 +60,8 @@ public:
 		NOTIFICATION_WM_ABOUT = 1011,
 		NOTIFICATION_CRASH = 1012,
 		NOTIFICATION_OS_IME_UPDATE = 1013,
+		NOTIFICATION_APP_RESUMED = 1014,
+		NOTIFICATION_APP_PAUSED = 1015,
 	};
 
 	virtual void input_event(const Ref<InputEvent> &p_event);