Adjustments to handles visuals and behavior

- Fix display on devices with larger corners by resizing the handle
views as the corner radius changes.
- Fix home x assist handle color matching by ensuring `isListening` is
set to after color matching start
- Allow UiController to suppress handles showing up during assist
sessions by calling ScreenDecorations.setAssistHintBlocked
- Add animation curve from spec to handle scale animation
- Fix handle rounded ends
- Make handle dimensions customizable

jamesoleary 2 CLs - ag/7727795, ag/7727797 (fix test failure)
mrcasey 2 CLs - ag/7704742, ag/7713549

Test: Verify WAI
Bug: 130642504
Change-Id: I9563d7f437064c8c63c988a9fda41be906064219