Changed rounded rect paths from paths to rounded rects

We were creating custom paths that were used to clip
notifications at times and could lead to a janky experience.
Using the addRoundedRect call with cornerradii is more performant
and is much more straight forward to use.

Fixes: 159427252
Test: add notifications, scroll, observe normal clipping behavior
Change-Id: Id8e38cf72af7e9d27bee884ae37d0e27e75202f0