[audio] Refactor shared track logic

MMAP tracks currently don't inherit from the IAfTrack interface, so
there is duplication between MmapTrack and Track.

Pull out common logic into AfPlaybackCommon, which represents operations
associated with playback tracks which aren't tied to the audioflinger
mix/data-path implementation. The track interfaces directly inherit from
this class (virtually) so that these operations are accessible from the
associated threads.

 - playback hardening
 - port volumes/port mute
 - mute event notifications to AudioService

Bug: 241533526
Flag: EXEMPT mechanical refactor
Test: Oboe tester playback hardening MMAP and legacy
Test: dumpsys audio for mute events
Change-Id: I8de2d48b94b46fa0111622fb6856153ec067db25