Consider the previous unique state of an element during interruptions

This CL ensures that we better support interruptions when an element is
going away but then reappears in a new transition. This can often
happen with dual shade if one shade is being closed while we open the
new one.

Bug: 373799480
Test: ElementTest
Flag: com.android.systemui.scene_container
Change-Id: I5e7cb3fe39cca052e913691aee61d49feee85a6f