Merge "notification stack scroller doesn't need a11y focus" into sc-dev am: 49c7bc6618 am: 1ab91ceac2

Original change: https://googleplex-android-review.googlesource.com/c/platform/frameworks/base/+/15692791

Change-Id: I6f86a25fb5c62745aa406961b25431e1dfbd9442