Explicitly restart audio processing when switching active device

* Add internal APIs to restart A2DP session and use them
  when switching the A2DP active device:
  btif_a2dp_source_restart_session() and btif_a2dp_sink_restart_session() .
* Removed internal A2DP Source APIs that shouldn't be APIs
* Call immediately btif_a2dp_on_stopped() when processing
  BTIF_AV_STOP_STREAM_REQ_EVT event to stop sooner the audio
  datapath processing and report back to the Audio HAL call.
  This eliminates the need for waiting for the BTA_AV_STOP_EVT
  upcall event from the remote device.
* Added extra log information when processing events in the BtifAv
  state machine.

Bug: 78360113
Test: Manual: streaming A2DP, change active device, change codec setup.
Change-Id: Icb356587af9cfaee7aea9f3f9bc95a0fe000fc52
Merged-In: Icb356587af9cfaee7aea9f3f9bc95a0fe000fc52
(cherry picked from commit c7a5e6038a1c01de1a2219659f999e91003af598)