Merge "Use LayoutManager.onLayoutCompleted as a signal that content has changed" into sc-dev am: d541300f0e

Original change: https://googleplex-android-review.googlesource.com/c/platform/packages/apps/Launcher3/+/14939014

Change-Id: I24735139b97aaadaf5f85c76e44b1f94b08aa031