Hydrate ShadeExpansionStateManager

Unfortunately, now that we know ScrimShadeTransitionController is
relied on by more than NPVC, we have to preserve it and its dependency
ShadeExpansionStateManager as NPVC side effects for now. This change
also removes dragDownAmountPx from ShadeExpansionStateManager, since
all references to it are now gone.

Flag: ACONFIG com.android.systemui.scene_container DEVELOPMENT
Test: Updated and ran affected tests
Test: Manual
Bug: 303267342
Change-Id: I16549d129157ee4bff94e63e00d46eda042c6f54