Merge "notification stack scroller doesn't need a11y focus" into sc-dev am: 49c7bc66 am: 0e3a87bc am: 16699a13

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

Change-Id: Id8427301dfdca3d26f47d6150f7d4f3f9a535fbf