Refactor syncing between communal STL state and KTF

This introduces a new CommunalSceneTransitionInteractor which handles
syncing between the two state machines.

Similarly, it introduces new APIs for callers to set the desired KTF
state when changing scenes programatically.

Bug: 327225415
Test: atest CommunalSceneTransitionInteractorTest
Flag: com.android.systemui.communal_scene_ktf_refactor
Change-Id: If5a6165713a2933be92730bcb8321393700e0ba1