如何在flutter中用AppBar创建带箭头标记的弹出窗口，而不需要任何插件？

import 'package:flutter/material.dart';

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        appBar: AppBar(
          title: Text('Flutter Popup Menu'),
          actions: [
            PopupMenuButton(
              itemBuilder: (BuildContext context) {
                return [
                  PopupMenuItem(
                    child: Text('Option 1'),
                    value: 'option1',
                  ),
                  PopupMenuItem(
                    child: Text('Option 2'),
                    value: 'option2',
                  ),
                  PopupMenuItem(
                    child: Text('Option 3'),
                    value: 'option3',
                  ),
                ];
              },
              onSelected: (value) {
                // 处理选中的选项
                print('Selected: $value');
              },
            ),
          ],
        ),
        body: Center(
          child: Text('Hello, Flutter!'),
        ),
      ),
    );
  }
}