MediaSession2: Refactor incoming binder calls to the MediaSession2Stub

This CL refactors methods in MediaSession2Stub that handles incoming
binder calls from the controller by adding methods to do followings
in one place.
  1. Check if the session hasn't closed.
  2. Check if the controller is allowed for the command
  3. Call SessionCallback#onCommandRequest() for APIs that would be
     sent directly to the MediaPlayerBase or MediaPlaylistAgent if
     allowed.

This CL also adds missing command code for setRating().

Bug: 74581821
Test: Run CTS tests with MediaComponents/runcts.sh
Change-Id: I22ba0eae11b6b63b96b56abebf350b223faf4d39