UX polish for the quick affordance picker. am: d6772973e0 am: 643570f672

Original change: https://googleplex-android-review.googlesource.com/c/platform/packages/apps/ThemePicker/+/20946745

Change-Id: I1042f04a0e681c21048cf72ba34ad36dc933b5c9
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>