Add telecom support for multi-endpoint.

- Add "isExternalCall" method to Call class.
- Ensure CallAudioManager ignores external calls.
- Prevent InCallController from passing extras to InCall UI which cause
it to start displaying the fullscreen outgoing call UI.

Bug: 27458894
Change-Id: I40160edd6191e71b409ff1f18ca2b8cc9662211f