[flexiglass] Fix HUN alpha during Gone -> Shade transition

In Flexiglass we need a new way of getting the tracked row object from HeadsUpTouchHelper to NSSL, as the legacy path was through NPVC. This can now be done through NSSLC. In addition, we need the Z translation of the HUN to fade gradually as the shade expands, and remain higher than the rest of the stack throughout the transition to maintain the correct alpha.

Bug: 357661886
Test: manually verified that the HUN alpha is correct and drop shadow transitions gradually during the scene transition to Shade
Flag: com.android.systemui.scene_container
Change-Id: I3379d978019476972f78e1813f4f1c12bbf15c37