MediaSession2/Controller2: Add playlist support

This CL implements following APIs:
 - MediaSession2.get/setPlaylist
 - MediaController2.getPlaylist
 - MediaController2.ControllerCallback.onPlaylistChanged

Bug: 72537268
Test: Passed MediaSession2Test
Change-Id: I206bb1018cde38d7db296df0912d02272fe1c6c7
7 files changed