Bluetooth: Fix HFP SCO logic and documentation

AudioService:
* Call setBtScoActiveDevice and setBluetoothScoOn both in AudioService's
  broadcast receiver so that these two methods must be triggerred in
  the same sequence as ACTIVE_DEVICE_CHANGED and AUDIO_STATE_CHANGED
  intents are sent and we no longer need to handle race condition by
  synchronously checking active device in setBluetoothScoOn
* Default sco audio mode when no headset is active should be virtual
  voice call, as many HFP devices do not accept SCO audio without an
  ongoing call
* Synchronize checkScoAudioState() method with mScoClients
* Add helper functions connectBluetoothScoHelper and
  disconnectBluetoothScoHelper to call various SCO setup and tear down
  methods based on sco audio mode
* Try raw, virtual call, and voice recognition mode when disconnecting
  externally started SCO
* Add new sco state SCO_STATE_DEACTIVATING to allow back to back calling
  of startBluetoothSco and stopBluetoothSco

Audio Manager:
* Modified AudioManager logic so that removed devices callback is called
  before newly added devices

BluetoothHeadset:
* Modified BluetoothHeadset so that start and stop SCO using virtual
  voice call no longer need a parameter and will use active device by
  default
* Modified documentation around various sco mangement APIs to match
  their expected behaviors

Bug: 76114959
Test: VoIP calls sanity test cases
Change-Id: Id50db88f4ff36069b0f392c81dd9d90c24cd2206