docs: enable contextIsolation in fiddles (#39613)

docs/fiddles/native-ui/notifications/index.html

@@ -59,9 +59,6 @@
       </div>
     </div>
 
-    <script>
-      // You can also require other files to run in this process
-      require("./renderer.js");
-    </script>
+    <script src="renderer.js"></script>
   </body>
 </html>

docs/fiddles/native-ui/notifications/main.js

@@ -9,11 +9,7 @@ function createWindow () {
   // Create the browser window.
   mainWindow = new BrowserWindow({
     width: 800,
-    height: 600,
-    webPreferences: {
-      contextIsolation: false,
-      nodeIntegration: true
-    }
+    height: 600
   })
 
   // and load the index.html of the app.