Merge "Notify when quickstep gesture starts" into sc-dev am: 1f9fcf87f7 am: e50a7f54f8 am: d0823b4a14

Original change: https://googleplex-android-review.googlesource.com/c/platform/packages/apps/Launcher3/+/14630659

Change-Id: Id4c3d775648d64ef2aaa6fb2328796fbde0f7887