LS Wallpaper Sampling for Clock

Refactoring RegionSampler implementations (LS clock) to
properly sample from lockscreen wallpaper since it is no longer an image
view.

This also addresses previously known inconsistent behavior when determining color for small clock versus large clock. The small clock only changes visibility while the large clock's view is fully removed and added when active. Because of this, the small clock doesn't trigger our layout change listener like the large clock does, which causes it to not get re-sampled right away. To address this, there is now a special case handling to re-sample when the visibility of the small clock changes.

Flag: region_sampling
Bug: 265968912
Test: manual, atest RegionSamplerTest
Change-Id: I563b32ccfe2e25a2753779bb955171c714c84207