Force relayout when wallpaper engine become visible.

After 9118c9b5 the surface can be destroy after the window state become
invisible, since WallpaperService copy the surface from WMS and it is
not implement with ViewRootImpl, WallpaperService#Engine should call
relayout to get new surface when client need to redraw it.

Bug: 158955956
Test: verify the wallpaper can show by launch LiveWallpaperChange with
live wallpaper and push/pull it from recents several times.
Test: atest WallpaperServiceTest ImageWallpaperTest

Change-Id: I79f97df61696eea325183e9b9057cbb10ce8cc66