Add function set CallVideoClient on the CallVideoProvider.

- Added implementation of RemoteCallVideoClient.
- Filled out the proxy methods on RemoteCallVideoProvider.
- Renamed methods on CallVideoClient/CallVideoProvider. Per Santos's
advice, this is to distinguish between the methods handling remote
communication, and the actual implementation of those methods.

Bug: 15893156
Change-Id: I5f433db1faa820dc96913091ce09938ddf40ffdd