Add session ID return for QMediaPlayer on Android

The Visualizer class on Android requires MediaPlayer session ID to display music data from particular player. Without this ID only output mix can be got from Visualizer(0). This ID can be acquired by MediaPlayer.getAudioSessionId() call. But in current Qt implementation it cannot be transmitted from Java code to application. I suggest add this functionality.

Another possible solution is - set session ID to MediaPlayer while creating or later by call MediaPlayer.setAudioSessionId(int id). In this case first some session ID must be got from AudioManager then used in Visualizer(id) creation. Later it bind Visualizer with MediaPlayer.

Now there is no way to bind Visualizer and Android MediaPlayer used by QMediaPlayer.