Add Wallpaper.getBitmapAsUser()

Add a new API to allow a wallpaper bitmap to be obtained for
a specific user.

Without this API, using only getWallpaperFile(..., userId), one
can't get a default wallpaper bitmap if the wallpaper is not set.

Bug: 25185253
Change-Id: Ibe1e9a49d22bee08fd4bed415573c1ee28526aea
2 files changed