Self-Managed Incoming Call Disambiguation UX.

- Handle auto-disconnect of foreground call when answering a self-managed
call.
- Enforce restriction that the PhoneAccount associated with a self-managed
CS must have a label which is the app's name.
- Ensure self-managed phone accounts can't be registered with
call provider, connection manager, or sim sub capabilities.
- Add "incoming call" UX which is shown when a new incoming call from a
self-managed CS comes in and there is an existing call for another CS.

Test: Unit, manual
Bug: 34159263
Change-Id: I371be9baa6f56c77aa83349977c0131f0e319047