Merge "Animate taskbar background alpha and visibility alpha" into sc-dev am: 6d46fff269 am: dd1f1b0b08

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

MUST ONLY BE SUBMITTED BY AUTOMERGER

Change-Id: Ibbd7ca5ef7b54556a755c139aa90be50abcf68a0