PlayerBase: fix deadlock

Source of deadlock between PlayerBase.mLock and
  PlaybackActivityMonitor.mPlayerLock:

android.media.MediaPlayer.release()
> android.media.PlayerBase.baseRelease()
  > synchronized (mLock)
    > com.android.server.audio.PlaybackActivityMonitor.releasePlayer()
       > synchronized(mPlayerLock)
and:

com.android.server.audio.PlaybackActivityMonitor.unmutePlayersForCall()
> synchronized (mPlayerLock)
  > android.media.PlayerProxy.setVolume()
    > android.media.PlayerBase$IPlayerWrapper.setVolume()
      > android.media.PlayerBase.baseSetVolume()
        > synchronized (mLock)
          playerSetVolume()

Since system_server can have its own players, the calls to
 AudioService from PlayerBase can be synchronous, hence the
 deadlock.
The fix consists in never holding the lock in PlayerBase
 while calling into AudioService.
Refactor the playstate update into a method used for
 start / stop / pause.

Bug: 72294559
Test: see bug

Change-Id: I6451aa3bf19a0365472ba007b116a9e6151ab33e