Adds android.media.HwAudioSource class

The new HwAudioSource (inherits PlayerBase) serves as a player backed by
a hardware audio source device.

Sample usage

```
HwAudioSource player = new HwAudioSource.Builder()
        .setAudioDeviceInfo(deviceInfo)
        .setAudioAttributes(new AudioAttributes.Builder()
                .setUsage(AudioAttributes.USAGE_MEDIA)
                .build())
        .build();
player.start();
```

Bug: 112161027
Test: Launch FM Tuner application
Change-Id: Id1f49c88cbbdb2b9156137ed8920713aa29b2d1c