Restore new SurfaceView background implementation.

A previous commit reverted the new SurfaceView background implementation
due to a Z-ordering issue (where previously the backgrounds were below
ALL SurfaceView rather than EACH SurfaceView). It's easier to solve this
with relative layering as this CL does, and then we can keep the new implementation.
The new implementation has some other bug fixes in it too (see linked bug
w.r.t to setZOrderOnTop) and so it's a win.

Bug: 132353087
Test: SurfaceViewSurfaceValidator
Change-Id: I07b6e601e57fce3adb8e5ea8e173c7d7904422ca