Add Transition.progressTo(ContentKey)

This CL adds convenience method Transition.progressTo(), which I found
can be useful when used together with isTransitioningFromOrTo() or
isTransitioningBetween().

Bug: 373799480
Test: atest SceneTransitionLayoutStateTest
Flag: com.android.systemui.scene_container
Change-Id: I797fb1c69808d03ffb4b97fbfe2687819ede68bb