Fixing flakyness in widget tests

For some predicted app widgets, the layout happens before the recyclerView
can layout completely (because of preview layout invalidation), causing the
scroll cache to get in a wrong state.
Checking for scroll cache validity everytime instead of only during
data changes

Bug: 255797215
Test: Verified by hardcoing the chrome widget as predicted widget
Change-Id: Id2c68560baa45de89e08c53bdb9ee6820eab68c4