[Predictive Back] Widget to home polish: show extra rows at bottom during animation

1. setClipChildren(false) for WidgetFullSheet and content view during animation
2. setClipToOutline(true) for WidgetsRecyclerView and provide ViewOutlineProvider to expand bottom by 5% of height
3. Override calculateExtraLayoutSpace() for ScrollableLayoutManager
4. Manually modify AbstractSlideInView#mContent's background drawable during scale animation

bug: b/260956481
Test: manual

Change-Id: Ic391639de887cf4a70bc4965dc0b1fd9bc12dd2c