Audio focus: SDK/System API updates

Addressed API council notes: document some missing default values
  of AudioFocusRequest builder, remove getters on lister and
  handler.
Fix missing support of custom Handler for focus listener.
Integrate focus lock feature from AudioManager SystemAPI into
  new AudioFocusRequest class and builder. Deprecate system
  methods for focus requests that don't use AudioFocusRequest
Switch to a ConcurrentHashMap in AudioManager instead of a
  lock and HashMap to maintain the list of focus listeners
  for each AudioManager instance.
Clean up: all local IAudioService references can be made final.
  Add missing @Override for the Stub implementations.

Test: cts-tradefed run cts -m CtsMediaTestCases -t android.media.cts.AudioFocusTest
Bug: 30258418

Change-Id: I9e903379a607c723a2620821200547de679231d1