MediaSession2: Implement setPlayer

This CL makes controller's onPlaybackInfoChanged() be called whenever
the session calls setPlayer().
Also, it replaces all usages of VolumeProvider with VolumeProvider2.

Bug: 72616099
Test: Passed MediaSession2Test
Change-Id: I51f48f49e8d2ee369571de0ef48353750a0612be
8 files changed