Make active device change asynchronous. Restructure A2DP active device change API for clarity and speed. Merge active device and device config change handlers. Fix bug for a new A2DP device connection with handleBluetoothA2dpActiveDeviceChange. Bug: 122944517 Test: still needs Bt side using new interface Change-Id: Ia2fa6b2c98ed4452880e8abca4a069b904f8cc68