Enable multi-sim support in assisted dialing.

* Add a new flag to enable or disable multi-sim support.
* Add a new mock method to the ShadowTelephonyMananger to support N+.
* Use new O+ API when available.

This logic is client specific, and is unecessary in the platform.

Bug: 69861007
Test: new unit tests
PiperOrigin-RevId: 179970674
Change-Id: Id9889c81e3c196f4a246f0a604d08b81cc906499