docs: fix fiddles (#39060)

* refactor: replace Array.prototype.forEach.call with plain for-of

* fix: add missing contextIsolation: false

* fix: open links in default browser

docs/fiddles/menus/customize-menus/main.js

@@ -294,6 +294,7 @@ function createWindow () {
     width: 800,
     height: 600,
     webPreferences: {
+      contextIsolation: false,
       nodeIntegration: true
     }
   })