Make HearingAid code more generic

-group hearingAid code into HearingAidDeviceManager
-add subDevice in CachedBluetoothDevice to store second hearingAid device
-add test case

Bug: 112735753
Test: make -j42 RunSettingsLibRoboTests
Change-Id: I6f554076b3e4e525959aba84e735b15f0e55d9d3
11 files changed