AudioDeviceVolumeManager and VolumeInfo API changes

Context service name for accessing AudioDeviceVolume manager.
Add support in VolumeInfo to know whether it carries an explicit
  mute/unmute information (vs just default value of isMuted()).

Bug: 244326361
Test: atest android.media.audio.cts.AudioDeviceVolumeManagerTest
Test: atest android.media.audio.cts.VolumeInfoTest
Change-Id: Id718fbd7e0d5795ac480d9188faad4a70fba9808
Merged-In: Id718fbd7e0d5795ac480d9188faad4a70fba9808