AudioDeviceBroker in audio service

New AudioDeviceBroker class running in audio service.
Has dedicated message loop for handling audio device
   connections and disconnections.
New helper classes for AudioDeviceBroker:
 - BtHelper for Bluetooth
 - AudioDeviceInventory to manage list of devices

Bug: 112863932
Test: media CTS + audio CTS Verifier
Change-Id: I3e8f662a9d82fa7245695888e14fac7f4fc6e728