Merge "UX polish for lock screen preview (3/3)." into tm-qpr-dev am: af546e7c9d

Original change: https://googleplex-android-review.googlesource.com/c/platform/packages/apps/ThemePicker/+/21073324

Change-Id: I0951857c667bbc8897ef8304da70d7f5e87bed87
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>