Implement support for Absolute Volume Control

- Adds logic for enabling or disabling AVC. This is checked whenever one
  of the necessary conditions for AVC changes.
  (HdmiControlService#checkAbsoluteVolumeConditions)
- Adds code for listening for audio status changes from AudioService
  when using AVC (HdmiControlService#AbsoluteVolumeChangedListener).
- Adds code for notifying AudioService of volume changes on the System
  Audio device (HdmiControlService#notifyAvcVolumeChange,
  HdmiControlService#notifyAvcMuteChange)
- Adds action for querying and monitoring the audio status of the System
  Audio device (AbsoluteVolumeAudioStatusAction).
- Removes SystemAudioStatusAction: it is no longer needed because we
  use full volume when in System Audio Mode, and don't track audio status.

Test: atest PlaybackDeviceToAudioSystemAvcTest
PlaybackDeviceToTvAvcTest TvToAudioSystemAvcTest
Bug: 205817429

Change-Id: I4d7772de851b12085bb2e9844a41d52245ee1d4a