Metrics: Log A2DP playback related metrics through StatsLog

* BluetoothActiveDeviceChanged event for A2DP, HFP, and HEARING_AID
* BluetoothA2dpPlaybackStateChanged event
* BluetoothA2dpCodecConfigChanged event
* BluetoothA2dpCodecCapabilityChanged for selectable capability that is
  defined as capability supported by both Android and remote device

Bug: 112969790
Test: unit test, test drive with statsd
Change-Id: Iaff053536d4802e0780303382203e51150df98bb