Companion App Manages Connectivity State Interfaces

Created two new APIs in CompanionDeviceManager:
notifyDeviceAppeared and notifyDeviceDisappeared for
companion apps report connectivity.

Create a new callback method for user to override when
device is connected and disconnected

Bug: 199435613
Test: atest CtsCompanionDevicesTestCases

Change-Id: I6884d085cf810fdd42466d620e888b07367c9b94