docs: Adds Dialogs Fiddle example (#20473)

docs/fiddles/native-ui/dialogs/save-dialog/main.js

@@ -0,0 +1,66 @@
+// Modules to control application life and create native browser window
+const { app, BrowserWindow, ipcMain, dialog } = require('electron')
+
+// 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.
+let mainWindow
+
+function createWindow () {
+  // Create the browser window.
+  mainWindow = new BrowserWindow({
+    width: 800,
+    height: 600,
+    webPreferences: {
+      nodeIntegration: true
+    }
+  })
+
+  // and load the index.html of the app.
+  mainWindow.loadFile('index.html')
+
+  // Open the DevTools.
+  // mainWindow.webContents.openDevTools()
+
+  // Emitted when the window is closed.
+  mainWindow.on('closed', function () {
+    // Dereference the window object, usually you would store windows
+    // in an array if your app supports multi windows, this is the time
+    // when you should delete the corresponding element.
+    mainWindow = null
+  })
+}
+
+// This method will be called when Electron has finished
+// initialization and is ready to create browser windows.
+// Some APIs can only be used after this event occurs.
+app.on('ready', createWindow)
+
+// Quit when all windows are closed.
+app.on('window-all-closed', function () {
+  // On OS X it is common for applications and their menu bar
+  // to stay active until the user quits explicitly with Cmd + Q
+  if (process.platform !== 'darwin') {
+    app.quit()
+  }
+})
+
+app.on('activate', function () {
+  // On OS X it's common to re-create a window in the app when the
+  // dock icon is clicked and there are no other windows open.
+  if (mainWindow === null) {
+    createWindow()
+  }
+})
+
+ipcMain.on('save-dialog', event => {
+  const options = {
+    title: 'Save an Image',
+    filters: [{ name: 'Images', extensions: ['jpg', 'png', 'gif'] }]
+  }
+  dialog.showSaveDialog(options, filename => {
+    event.sender.send('saved-file', filename)
+  })
+})
+
+// In this file you can include the rest of your app's specific main process
+// code. You can also put them in separate files and require them here.