Introduce IRingtonePlayer, which handles playback for both Ringtone objects and Notifications. SystemUI now hosts this player, which it registers with AudioService. It also keeps MediaPlayer instances warm, and cleans them up after stop() or Binder death. Move both Ringtone and NotificationManagerService to play back audio through this new interface. Bug: 6376128, 6350773 Change-Id: I1dcb86d16ee3c4f07cdb2248d33dcff4ead3609a