Add persistent state for Bluetooth high quality audio support

Defines the flags used in code and the Settings.Global key names for
persisting the following state for Bluetooth A2DP Sink devices:
-Whether the device supports optional codecs or not
-Whether optional codecs should be turned on for the device

For each of these two properties we model the state in the code as
yes/no/unknown, so that we can tailor the UI and behavior
accordingly.

Bug=37441685
Test: manually

Change-Id: I6bcd02fd7c95bef989575f3b13d4788dab61971a