XMonad.Prelude: add the WindowScreen type

`WindowScreen` is a type synonym for the specialized `Screen` type, that
results from the `WindowSet` definition in XMonad.Core. Having this type
defined and exported in a central module saves extension developers from
trying to reconstruct it, whenever the general `Screen i l a sid sd` is
not suitable.

Note: this should be moved to `XMonad.Core` in the next core release.

XMonad/Actions/EasyMotion.hs

@@ -271,7 +271,7 @@ handleSelectWindow c = do
         $ M.elems
         $ M.mapWithKey (\sid ks -> buildOverlays ks <$> sortedOverlayWindows sid) m
      where
-      screenById :: ScreenId -> Maybe (W.Screen WorkspaceId (Layout Window) Window ScreenId ScreenDetail)
+      screenById :: ScreenId -> Maybe WindowScreen
       screenById sid = find ((== sid) . W.screen) (W.screens ws)
       visibleWindowsOnScreen :: ScreenId -> [Window]
       visibleWindowsOnScreen sid = filter (`elem` toList mappedWins) $ W.integrate' $ screenById sid >>= W.stack . W.workspace

XMonad/Actions/Navigation2D.hs

@@ -388,7 +388,7 @@ data Navigation2DConfig = Navigation2DConfig
   }
 
 -- | Shorthand for the tedious screen type
-type Screen = W.Screen WorkspaceId (Layout Window) Window ScreenId ScreenDetail
+type Screen = WindowScreen
 
 -- | Convenience function for enabling Navigation2D with typical keybindings.
 -- Takes a Navigation2DConfig, an (up, left, down, right) tuple, a mapping from