Update assisted dialing extras in preparation for platform implementation.

* Use only one extra as if we were going to make a request of the Platform.
* Modify the incallui to handle instances where the platform may not supply TransformationInfo.

This should accommodate instances where the platform "used" assisted dialing,
but did not provide the necessary TransformationInfo.

Test: unit tests
PiperOrigin-RevId: 179841752
Change-Id: I06411dc00812dba8978a2a090d8769dcce9b2ad6