Merge "Support dark theme in wallpaper launcher preview." into sc-v2-dev am: ca74b4d5be am: 720795a039

Original change: https://googleplex-android-review.googlesource.com/c/platform/packages/apps/Launcher3/+/15694616

Change-Id: I8b31956d2f269f2d20fb03518fa9e297bad04e65