Merge "Add a header container view to the widgets full sheet" into sc-dev am: 21803095ee

Original change: https://googleplex-android-review.googlesource.com/c/platform/packages/apps/Launcher3/+/13687970

MUST ONLY BE SUBMITTED BY AUTOMERGER

Change-Id: I737a9e425e6d591cf561ac01c63b76df459db38f