Audio recording notification API

AudioService can register a recording callback with AudioSystem.
Callbacks are handled in a new class, RecordingActivityMonitor.
This class notifies registered AudioManager instances
  of updates, only if this AudioManager has client callbacks.
Each AudioManager dispatches updates to its registered
  callbacks.

Bug 22876530

Change-Id: I95c6e5ec0631e53af53a490bcecca96089490089