Merge "Setting/getting per-screen wallpaper (2/3)." into tm-qpr-dev am: 8ca34bc0d4

Original change: https://googleplex-android-review.googlesource.com/c/platform/packages/apps/ThemePicker/+/20920224

Change-Id: Id4684864aec4b6d9474b0e3fef385b5bf88aa2d3
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>