JAudioTrack: Add offload mode support

Also, this CL adds below methods to JAudioTrack:

1) getAudioSessionId

2) setOutputDevice
  - However, it uses a hidden method of AudioManager.
    (See MediaPlayer2Impl.java)

3) getFlags
  - Method body is incomplete.
  - It needs a way to check whether the audio track is direct,
    or whether the HW supports A/V sync.

4) getTimestamp(ExtendedTimestamp *timestamp)
  - Method body is empty.
  - It needs appropriate Java method to call.
  - This is a different method from previously added method
    getTimestamp(AudioTimestamp& timestamp).

5) pendingDuration
  - Method body is incomplete.
  - It depends on above getTimestamp method.

6) add/removeAudioDeviceCallback
  - Method body is empty.
  - It needs appropriate Java method to call.
  - Cannot use Java AudioTrack.addOnRoutingChangedListener(), since the
    callback onAudioRoutingChanged(AudioRouting) does not provide the
    audio_io_handle_t which the native AudioDeviceCallback needs.

Bug: 70363744
Test: Builds successfully
Change-Id: I50455280812546d97f2c3e6425d17c0483476af1