Merge "Update dismiss appearance and add scrim per UX mocks." into rvc-dev am: a65d7258 am: 81d8cabe am: e21dca95

Original change: https://googleplex-android-review.googlesource.com/c/platform/frameworks/base/+/11683086

Change-Id: I1e8dcaf1df8f259ea2d4f7a3185a184edc32a60a