Fixes #2022, do not resume on Android when surfaceChanged

If the app is in landscape mode and the user presses the power button, a pause
is followed immediately by a surfaceChanged event because the lock screen
is shown in portrait mode. This triggers a "false" resume.
So, we just pause and resume following the onWindowFocusChanged events.

Also, wait for SDL_APP_WILLENTERBACKGROUND and SDL_APP_DIDENTERBACKGROUND before
blocking the event pump.

android-project/src/org/libsdl/app/SDLActivity.java

@@ -695,11 +695,6 @@ class SDLSurface extends SurfaceView implements SurfaceHolder.Callback,
             SDLActivity.mSDLThread = new Thread(new SDLMain(), "SDLThread");
             enableSensor(Sensor.TYPE_ACCELEROMETER, true);
             SDLActivity.mSDLThread.start();
-        } else {
-            // The app already exists, we resume via handleResume
-            // Multiple sequential calls to surfaceChanged are handled internally by handleResume
-
-            SDLActivity.handleResume();
         }
     }