windowPreview: Don't hide overlay while hovering icon

We should treat the icon like we do the caption or close button,
and still consider the preview hovered when the pointer is over
the icon.

Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/3049>
(cherry picked from commit 39d2988865)

js/ui/windowPreview.js

@@ -569,6 +569,7 @@ var WindowPreview = GObject.registerClass({
             GLib.PRIORITY_DEFAULT,
             WINDOW_OVERLAY_IDLE_HIDE_TIMEOUT, () => {
                 if (this._closeButton['has-pointer'] ||
+                    this._icon['has-pointer'] ||
                     this._title['has-pointer'])
                     return GLib.SOURCE_CONTINUE;