[flexiglass] Fix surfaceBehindVisibility

Fix another flicker that happens because surfacebehindVisibility is
switching to off too quickly. It seems that following the legacy
implementation and reusing defaultSurfaceBehindVisibility would suffice.
Even though isFinishedIn(Scenes.Gone) does work with flexiglass it does
not carry the same information as there are now Shade scenes.

We instead rely on lockscreenVisibilityWithScenes which does similar
things but also considers shade. Transition specific handling for
surfaceBehind do still apply.

Bug: b/353323341
Flag: EXEMPT bug fix
Test: Manual transition check
Change-Id: Ic5bc090760012a27f1ba3ab7d48ad949ef615b2b