[CS] Make NotificationShadeWindowViewController a singleton.

Unfortunately, CentralSurfacesImpl and NSWVC have a lot of cross-talk
that's infeasible to remove right now, so this adds a Lazy<NSWVC> to
CSI.

This removes both NSWVC and NSWV from CentralSurfacesComponent.

Bug: 277762009
Test: smoke test of notification shade: verify it can be opened and
closed in portrait and landscape, you can interact with notifications,
it responds to theme change and font scale change
Test: atest CentralSurfacesImplTest

Change-Id: I43c85fd3e5ff7fcefbc269f64f9cdf835e50a8a3