Audio focus: framework enforces ducking

When an application requests audio focus with AUDIOFOCUS_GAIN_TRANSIENT_MAY_DUCK
 automatically duck any active players of the current focus owner, unless:
 - the player is a SoundPool
 - the player plays content of type AudioAttributes.CONTENT_TYPE_SPEECH
 - the focus owner requested focus with an AudioFocusRequest which
    returns true for willPauseWhenDucked().
 - the focus owner and requester share the same UID

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

Change-Id: I997905089252be410d58e03b350b6aa8a0d98e61