Merge changes from topics "mutable-stl-state", "stl-punch-hole" into main

* changes:
  Remove Element.lastSharedState and SceneState.lastState
  Remove Modifier.punchHole in SceneScope (1/2)
  Remove SceneTransitionLayoutImpl.readyScenes
  Introduce MutableSceneTransitionLayoutState
  Move onChangeScene and transitions to STLState (1/2)