New API to specify an accessbility service wants to force ducking
in its focus request, regardless of the framework's evaluation
of whether or not it should duck the other players.
Use of this API is restricted to requests coming from services
bound to the A11y service, or root
Bug: 62194333
Test: play a podcast in GPM and "adb shell claf --gain 3 --usage 11 --forceDuck"
Change-Id: I85f26afa14fe233a3b870f86c9084613203494b8
9228af6bc2