Send a command to the wallpaper when re-applying it

We don't set a wallpaper component again if it's the one
already set, so we're now sending it a command notifying
of this in case the wallpaper needs to reload or apply
settings.

Bug: 147677688
Test: atest WallpaperManagerServiceTests
Change-Id: If65671287ba3270933b75771a8c1c65c5ff0216a