Clean up BluetoothMediaBrowserService interfaces

This change cleans up several small things in our media browser service:
  - Refactor several of the methods called to send our service info so
    its clear what info we're sending in code
  - Break up now playing queue updates and browse node updates into
    separate functions
  - Strengthen and standardize the method to access our singleton
  - Remove uncalled functions, like play() and pause()
  - Standardize logging for when our singleton isn't available

Flag: EXEMPT, mechanical refactor only
Bug: 350502412
Test: atest AvrcpControllerStateMachineTest.java
Change-Id: I6d853f00960557049297cc1112c1058de1988b5c