Move notification shade changes into GX Overlay.

* Reduce horizontal margins and padding for shade
* Restore old dismiss rest behavior
* Restore notification background
* Hide the 'two radii' new feature (small radius now 0)
* Reduce notification divider height

Test: manual inspection w/ and w/o overlay
Test: atest NotificationRoundnessManagerTest
Test: atest NotificationMenuRowTest
Fixes: 175710408
Fixes: 178609228
Change-Id: I3e3e6359a8afb7d9f07a1922c3f884901e16e458