[flexiglass] Shade scene view-models are SysUiViewModel

As per go/sysui-arch:summer-24

Bug: 354270224
Flag: com.android.systemui.scene_container
Test: new unit test, updated existing unit and integration tests
Test: manually verified that the shade scene can navigate from/to adjacent scenes
and that its elements seem to animate and render correctly

Change-Id: I2e1fb128555006a47743b1b6e89b3aabc56c8a0e