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

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

Change-Id: I1f3da7b95d85e0111433afcf64c87284ba261dbe