Add sendTransitionStepsOnStartTransition.

Currently, calls to startTransition are recorded/spied on so that we can verify that someone asked to start a transition.

However, as our interactors become more complicated, calls to startTransition sometimes are guarded by checking previous TransitionSteps. This requires us to send the appropriate fake transition steps prior to triggering the startTransition call we're looking for.

To improve this, and also test more live code, this adds support for sending STARTED/RUNNING/FINISHED steps in response to startTransition calls from the real interactors.

Also, adds FromLockscreenTransitionInteractor tests as promised in the previous CL.

Bug: 370177430
Test: atest SystemUITests
Flag: EXEMPT tests
Change-Id: Iab04c8799978b54568a1069c8d7ce425bbe02a93