Re-enable and fix failing tests in NotificationStackScrollLayoutTest

Fixing some issues with tests:
 - mock ScreenOffAnimationController, because if we obtain a real
   one, it will register BroadCastReveivers
 - mock a res string, to avoid NPEs
 - update a matcher
 - delete the @UiThreadTest annotations, because it was overwritten by
   the SysuiTestCase#mLooperRule anyways
 - delete #testAppearFractionCalculation(), because its content is no
longer relevant: we just return a value from
AmbientState#getAppearFractionCalculation().

Fixes: b/284136971
Test: atest NotificationStackScrollLayoutTest
Test: run with abtd to assure we have no flakiness
Change-Id: I044e96db2ad547bad00203ee26cf619fa95ec05e