[Flexiglass] Fix split shade layout and transitions

Cleans up split shade layout and implements gone -> split shade transition and overscroll behavior. Remaining work includes: verifying padding of shade header (the corner radius value sometimes does not appear to be correct at the moment), fixing QS tiles being a pixel off causing them to peek out from behind the notif scrim, and fixing notif scrolling.

Bug: 338080993
Test: visually verified all shade scene transitions on foldable
Flag: ACONFIG com.android.systemui.scene_container DEVELOPMENT
Change-Id: Idde17ffb9064cfd3675fba42f1e6f928092e9781