dbusServices/extensions: Override destroy() method

Some extensions try to destroy the provided dialog, so they can
instead show the preferences in an alternative way.

Unfortunately that is undetectable from the Extensions service,
which still thinks the dialog is open, and will therefore block
other prefs dialogs.

Try to steer extensions away from that anti-pattern (or at the
very least switch to `close()` which doesn't break) by overriding
the window's destroy() method and show an extension error instead.

Closes https://gitlab.gnome.org/GNOME/gnome-shell/-/issues/7435

Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/3209>

js/dbusServices/extensions/extensionPrefsDialog.js

@@ -58,6 +58,11 @@ export const ExtensionPrefsDialog = GObject.registerClass({
         });
     }
 
+    destroy() {
+        this._showErrorPage(
+            new Error('destroy() breaks tracking open dialogs, use close() if you must'));
+    }
+
     _showErrorPage(e) {
         while (this.visible_page)
             this.remove(this.visible_page);