SF: Clean up forced refresh and repaint

Remove the misleading repaintEverything flag from CE, as it only affects
debug flashes (and the fullscreen strobe during refresh rate transitions
is of dubious utility). It also causes GPU virtual displays to recompose
despite not being dirty, but forcing repaint can be done by invalidating
geometry instead.

Clean up the Scheduler/SF interface to schedule invalidate, refresh, and
repaint. Fix atomicity of a few debug variables.

Bug: 182939859
Test: Toggle "Show surface updates" in dev settings.
Test: libcompositionengine_test
Change-Id: I176d01cab43e5ab4697b762fe3172b09f4f3d202