Add tests for rendering to virtual displays.

Add parameterization when validating via screenshot to either...take a
screenshot, or instead render to a virtual display and lock that
surface.

Did not add parameterization to LayerUpdateTest + child test classes,
since there should be enough tets now that there's sufficient coverage
of doComposeSurfaces. Such paramterization could likely be added in the
future, however.

Bug: 119583189
Test: SurfaceFlinger_test
Change-Id: Ia984d1e6c8872f6f32c220ed4dca71ef68995d1e