docs: enable contextIsolation in fiddles (#39613)

docs/fiddles/native-ui/dialogs/open-file-or-directory/main.js

@@ -1,5 +1,6 @@
 // Modules to control application life and create native browser window
 const { app, BrowserWindow, ipcMain, dialog, shell } = require('electron/main')
+const path = require('node:path')
 
 // Keep a global reference of the window object, if you don't, the window will
 // be closed automatically when the JavaScript object is garbage collected.
@@ -11,8 +12,7 @@ function createWindow () {
     width: 800,
     height: 600,
     webPreferences: {
-      contextIsolation: false,
-      nodeIntegration: true
+      preload: path.join(__dirname, 'preload.js')
     }
   })
 
@@ -59,17 +59,11 @@ app.on('activate', function () {
   }
 })
 
-ipcMain.on('open-file-dialog', event => {
-  dialog.showOpenDialog(
-    {
-      properties: ['openFile', 'openDirectory']
-    },
-    files => {
-      if (files) {
-        event.sender.send('selected-directory', files)
-      }
-    }
-  )
+ipcMain.handle('open-file-dialog', async () => {
+  const options = {
+    properties: ['openFile', 'openDirectory']
+  }
+  return (await dialog.showOpenDialog(options)).filePaths
 })
 
 // In this file you can include the rest of your app's specific main process