Voice state + transcription in VoiceInteractionSvc

Voice state as well as voice transcription can be provided by the
VoiceInteractionService. These get proxied to the AssistManager which
can update the system UI to reflect the state & transcription.

Test: TBD
Bug: 122740752
Bug: 123080754
Change-Id: I79cac1d89fe0123bf25a05d551cb4ef40ae1368e