Merge "Animate taskbar background alpha and visibility alpha" into sc-dev am: 6d46fff269

Original change: https://googleplex-android-review.googlesource.com/c/platform/packages/apps/Launcher3/+/13438959

MUST ONLY BE SUBMITTED BY AUTOMERGER

Change-Id: I6b4657cb20fb5ed65f67fcf1414bf1724e533bf3