Merge "Fix some small related to back button alpha" into sc-v2-dev am: 75867ae0 am: 747dae3b

Original change: https://googleplex-android-review.googlesource.com/c/platform/packages/apps/Launcher3/+/16487030

Change-Id: I1392f9f16613ef9fb0add480260d9d5af3fbed16