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Add Session API calls to RCC and AudioManager

This makes RCC and MediaButtonReceiver (via AudioManager) also use the new Session APIs in parallel to their existing code. This will allow us to bring up the Session compatibility pieces without disrupting the old behavior and then switch everything over to just using the new APIs when ready.

Change-Id: I33ce0a044dea3ec763f2302b91a5e415be27d4a4