appDisplay/baseAppView: Also consider its own content box when adapting

Otherwise setting margins and paddings from CSS may result in the grid
being adapted to the wrong size.

Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/1519>

js/ui/appDisplay.js

@@ -848,6 +848,7 @@ var BaseAppView = GObject.registerClass({
             x2: width,
             y2: height,
         });
+        box = this.get_theme_node().get_content_box(box);
         box = this._scrollView.get_theme_node().get_content_box(box);
         box = this._grid.get_theme_node().get_content_box(box);