bass_client: Use proxy for Advertising Manager and BluetoothAdapter

This change would expose a proxy BluetoothAdapter methods and introduces
singleton Periodic Advertising Manager object for testability and
independence from real objects of those classes.

Tag: #feature
Bug: 322818333
Bug: 316005152
Test: atest BassClientStateMachineTest
Change-Id: I1b3599fb13529c84b07e7b85f2eb30728a063b98