windowManager: Add animations for maximize and unmaximize

The fullscreen animation code is now generic enough to handle any
size change animations, so stop limiting it to (un)fullscreen to
get animations on (un)maximize as well.

https://bugzilla.gnome.org/show_bug.cgi?id=766685

js/ui/windowManager.js

@@ -1313,9 +1313,7 @@ const WindowManager = new Lang.Class({
             return;
         }
 
-        if ((whichChange == Meta.SizeChange.FULLSCREEN ||
-             whichChange == Meta.SizeChange.UNFULLSCREEN) &&
-            oldFrameRect.width > 0 && oldFrameRect.height > 0)
+        if (oldFrameRect.width > 0 && oldFrameRect.height > 0)
             this._prepareAnimationInfo(shellwm, actor, oldFrameRect, whichChange);
         else
             shellwm.completed_size_change(actor);