Fix element elevation

This CL fixes element elevation so that the text in an element is
correctly drawn when that element is elevated. See b/374257277 for
details.

Bug: 374257277
Test: Manual, tested in the STL demo app
Flag: com.android.systemui.scene_container
Change-Id: I342b28f7d77b19e0be5a1969e55ce8913adcb315