[Flexiglass] Use SceneTransitionLayoutState methods

With the nested STL, querying the transitionState directly only checks
the innermost one. Instead, use the methods that allow to check for
ancestors.

Also, drive-by fixes of other uses of LayoutState in the inner scene.

Test: manual, scroll and collapse.
Bug: 437386478
Flag: com.android.systemui.scene_container
Change-Id: I56affb42a9c49f65e3d5a76dcfd3d03b18674011