Repository: flutter
Issue: [web] Option key shortcuts are broken on macOS
Labels: a: text input,framework,platform-web,has reproducible steps,browser: safari-macos,P2,found in release: 2.5,found in release: 2.6,browser: chrome-desktop,customer: troy,team-web,triaged-web

## Option Key not detected

It turns out that the **Option (or Alt) ⌥** key on macOS is currently not working for [`ShortcutActivator`](https://api.flutter.dev/flutter/widgets/ShortcutActivator-class.html) on macOS **on web**.

That is, any `shortcuts` that use the alt key do not work. That applies both to `SingleActivator` as well as `LogicalKeySet`; [`LogicalKeyboardKey.alt`](https://api.flutter.dev/flutter/services/LogicalKeyboardKey/shift-constant.html) simply seems to be broken. This happens to our users on Chrome using Macbook.

---

```dart
SingleActivator(
  LogicalKeyboardKey.keyA,
)
```

Is detected but:

```dart
SingleActivator(
  LogicalKeyboardKey.keyA,
  alt: true,
)
```

is not detected on macOS on web. All the other modifiers still work.

## Steps to Reproduce

1. Run `flutter create bug --platforms=web`.
2. Update `main.dart` as follows:

<details><summary>Click to expand code snippet</summary>

```dart
import 'package:flutter/material.dart';
import 'package:flutter/services.dart';

void main() {
  runApp(const MyApp());
}

class MyApp extends StatelessWidget {
  const MyApp({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Shift is broken',
      shortcuts: const {
        SingleActivator(
          LogicalKeyboardKey.keyA,
          control: true,
        ): PrintIntent(false),
        SingleActivator(
          LogicalKeyboardKey.keyA,
          alt: true,
        ): PrintIntent(true),
      },
      actions: {
        PrintIntent: CallbackAction<PrintIntent>(onInvoke: (intent) {
          if (intent.alt) {
            // This is never called.
            print('Alt is working');
            return;
          }
          print('Control is working.');
        }),
      },
      builder: (context, child) {
        return const Focus(
          autofocus: true,
          child: Placeholder(),
        );
      },
    );
  }
}

class PrintIntent extends Intent {
  const PrintIntent(this.alt);

  final bool alt;
}
```

</details>

3. Run `cd bug` and `flutter run -d chrome` on macOS.
4. Focus the window.
5. Press CTRL + A.
6. Press OPTION + A.

**Expected results:** `Control is working.` and then `Alt is working.`

**Actual results:** `Control is working.` only.

<details>
  <summary>Logs</summary>

```
Performing hot restart...
Waiting for connection from debug service on Chrome...
Restarted application in 374ms.
Control is working.
Control is working.
Control is working.
```

```
[✓] Flutter (Channel dev, 2.6.0-5.1.pre, on Microsoft Windows [Version 10.0.19042.1165], locale en-150)
    • Flutter version 2.6.0-5.1.pre
    • Upstream repository https://github.com/flutter/flutter.git
    • Framework revision f2903d3da5 (7 days ago), 2021-09-08 12:44:29 -0700
    • Engine revision 0bd9be379a
    • Dart version 2.15.0 (build 2.15.0-82.0.dev)


[✓] Chrome - develop for the web
    • Chrome at C:\Program Files (x86)\Google\Chrome\Application\chrome.exe

[✓] Connected device (3 available)
    • Chrome (web)      • chrome  • web-javascript • Google Chrome 93.0.4577.82
```

</details>

---

Note that when running **on Windows** on web, the _alt key **does**_ work.  
This is related to #90167.