Merge "Adding support for extending back behavior in Launcher" into tm-dev am: a292987030 am: d023ac2bee

Original change: https://googleplex-android-review.googlesource.com/c/platform/packages/apps/Launcher3/+/18187213

Change-Id: Iba3441adb20f3258a0e5ae88236e121c9d9beaec
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>