Allow clipping of notifications to be toggled.

There are two clippings being changed. The first is the shrinking of the
height when a notification is being scrolled offscreen. This effect is
not noticeable on phones/tablet, where the background is a rectangle.
However, for Android Auto, the background is a rounded rectangle. By
allowing the clipping to be disabled, the notification now appears to
scroll off-screen and not that its height is shrinking.

The second modification is to allow the outline of the notification to
have rounded corners. This allows the outline to clip its contents along
the rounded edges.

Test: booted up on phone and Android Auto headunit
Bug: 33210494
Change-Id: Id41a57c9164cabe554b4c5b4d713e9d3cb805b09