Always use the transition scene(s) when computing element values

This CL ensures that we always use the current transition of an element
when computing its values (size, offset, etc), even for scenes not
currently in the transition. Before this CL, it could happen that we
would use the wrong scene when computing the size of an element in a
scene during complex interruption scenarios.

Bug: 290930950
Test: ElementTest
Flag: com.android.systemui.scene_container
Change-Id: I860ee7049c0bfe989dd095899c745f787c207f2a