Simplify Surface recreation

Right now, when the app goes into background, the whole QtSurface aka SurfaceView is destroyed, and recreated again once the app comes back to foreground.

However, based on Android SurfaceView docs it should handle the destroying and recreation of the Surface it wraps by itself, so instead of destroying/recreating the whole SurfaceView every time, we could just listen to the SurfaceHolder callbacks to let us know when the Surface is valid and when not.