[flexiglass] Add NotificationStackView (NSV) interface

* NSV is implemented by NSSL so that we can eventually stop injecting NSSL/NSSLC everywhere.
* Remove the NotificationStackAppearanceInteractor from the NSSLC and bind all fields to NSV instead of NSSLC.
* Add SceneContainerFlag.assertInLegacyMode() to some NSSLC methods where the new code can go directly to NSV.
* Add ShadeScrimShape which includes the actual rounding radii, and have the ViewModel take the radius flow and position flow to expose that directly, moving that ViewBinder logic to the ViewModel.

Bug: 296118689
Test: atest SystemUITests
Flag: ACONFIG com.android.systemui.scene_container DEVELOPMENT
Change-Id: I87e6a5219c46f0cdbed569e004a016d6064fcc8f