Move 'Apply' string from ThemePicker to WallpaperPicker2 am: 2e0e1e8275 am: cb1622b067

Original change: https://googleplex-android-review.googlesource.com/c/platform/packages/apps/ThemePicker/+/16344704

Change-Id: I097335d2ed6bee0be68314d59a111c4a41aa15f0