[flexiglass] Fix Gone->QS Transition and HUN placeholder

Fixes Gone->QS transition and fixes shared element transition for HUN placeholder during Shade->QS transition

Bug: 330702510
Test: manually verified Gone/LS -> QS transition with and without active HUN
Test: added new unit test
Flag: com.android.systemui.scene_container
Change-Id: I05c16a1385877eddac67270984ff0af5fb01674f
4 files changed