Audio focus: fix notifying apps to pause without an external policy

In the absence of an external audio policy that implements ducking,
   check whether the focus loser has the
   AUDIOFOCUS_FLAG_PAUSES_ON_DUCKABLE_LOSS flag: if yes, do not
   let the framework handle ducking, notify the app.

Test: use app that calls AudioFocusRequest.Builder.setWillPauseWhenDucked(true) and verify it doesn't get ducked by framework
Bug: 30258418
Change-Id: I12655b413504ed101dd14d2b60ffdaf16c5b6148