Update notification view to match newer specs

- Use smaller radius for notifications round rect background
- Remove "Notifications" header, and clip children to round rect path
- Flip main notification so that icon shows on the right instead of
  left; footer is also flipped so animation makes sense
- Clean up animations to animate view outline instead of height

Bug: 32410600
Change-Id: I6bd1e1f8395b3703f28c3b0056a89e67672368ab