[flexiglass] QS scene view-model is a SysUiViewModel

As per go/sysui-arch:summer-24

Bug: 354270224
Test: unit tests pass
Test: manually verified navigation to/from QS scene
Test: manually verified that QS tiles and edit mode work
Flag: com.android.systemui.scene_container
Change-Id: I69854ee9eca3070b0c4f29db16419565f8957b54