Fix per-display flags propagation in flexiglass

Flags were only kept up to date for the default display, causing elements relying on them to broken on external displays (e.g. taskbar visibility)

Bug: 362719719
Bug: 417921986
Test: SceneContainerStartableTest
Flag: com.android.systemui.shade_window_goes_around
Change-Id: I970015c26cf43d542780b1eb09884769fe52b975