[flexiglass] Unfold transition support in the lockscreen scene.

When a foldable is fully unfolded and then the user begins to fold it
up, there's a subtle animation that happens to elements across the
screen. Left-hand side elements move to the right and right-hand side
elements move to the left, seeming to gently float towards the fold
hinge.

This CL adds that for Flexiglass, only for the split lockscreen scene.

Test: added integration test for the new code that exposes the
unfoldTranslations in the view-model
Test: manually verified that gently folding up the device correctly
slides the elements of the split lockscreen scene into the center (both left-hand
side elements and the NSSL on the right)
Flag: ACONFIG com.android.systemui.scene_container DEVELOPMENT
Bug: 330483283

Change-Id: I56fd548c8cd46f33094de6058c2fa2830dcce005