Add a BUILD file for the WallpaperPicker app. am: 55686c886d am: 64a86bd585 am: 24573416f9 am: ccebb27cf1

Original change: https://android-review.googlesource.com/c/platform/packages/apps/WallpaperPicker/+/1833217

Change-Id: Id330716c5c0d9a7b3cc2270efdae1df5cd8f1e39