Set FastBitmapDrawable's badge alpha when updating drawable alpha. am: 08f89425bb am: 43f230bcc8

Original change: https://googleplex-android-review.googlesource.com/c/platform/packages/apps/Launcher3/+/25058707

Change-Id: Ied1832fbaf8d95f23283e6e6201d97dfc41822f9
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>