Repository: flutter
Issue: [Semantics]Incorrect accessibility semantics on the `Table` widget
Labels: framework,a: accessibility,platform-web,a: desktop,has reproducible steps,P2,found in release: 2.10,found in release: 2.11,team-framework,triaged-framework

Hi,
When using the `Table` widget, accessibility information doesn't seem to be generated.

In particular when running the below code sample on Flutter Web, I cannot navigate the resulting table with standard screen reader commands (using NVDA), and NVDA does not know there is a table on the page.

```dart
import 'package:flutter/material.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: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: const MyHomePage(),
    );
  }
}

class MyHomePage extends StatelessWidget {
  const MyHomePage({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: const Text('People'),
      ),
      body: Table(
        children: const [
          TableRow(
            children: [
              TableCell(child: Text('First Name')),
              TableCell(child: Text('Surname')),
              TableCell(child: Text('Age'))
            ],
          ),
          TableRow(
            children: [
              Focus(child: TableCell(child: Text('Chris'))),
              Focus(child: TableCell(child: Text('Norman'))),
              Focus(child: TableCell(child: Text('32')))
            ],
          ),
          TableRow(children: [
            Focus(child: TableCell(child: Text('Mother'))),
            Focus(child: TableCell(child: Text('Earth'))),
            Focus(child: TableCell(child: Text('Pretty old')))
          ])
        ],
      ),
    );
  }
}
```

```shell
[ÔêÜ] Flutter (Channel master, 2.11.0-0.0.pre.871, on Microsoft Windows [Version 10.0.22000.556], locale en-GB)
    ÔÇó Flutter version 2.11.0-0.0.pre.871 at C:\Users\chris\flutter
    ÔÇó Upstream repository https://github.com/flutter/flutter.git
    ÔÇó Framework revision 4f4c7816c3 (6 hours ago), 2022-03-14 07:35:07 +0100
    ÔÇó Engine revision 6239bfb884
    ÔÇó Dart version 2.17.0 (build 2.17.0-182.0.dev)
    ÔÇó DevTools version 2.11.1

[ÔêÜ] Android toolchain - develop for Android devices (Android SDK version 31.0.0-rc2)
    ÔÇó Android SDK at C:\Users\chris\AppData\Local\Android\sdk
    ÔÇó Platform android-31, build-tools 31.0.0-rc2
    ÔÇó Java binary at: C:\Program Files\Android\Android Studio\jre\bin\java
    ÔÇó Java version OpenJDK Runtime Environment (build 11.0.10+0-b96-7249189)
    ÔÇó All Android licenses accepted.

[ÔêÜ] Chrome - develop for the web
    ÔÇó Chrome at C:\Program Files (x86)\Google\Chrome\Application\chrome.exe

[ÔêÜ] Visual Studio - develop for Windows (Visual Studio Enterprise 2022 17.1.0)
    ÔÇó Visual Studio at C:\Program Files\Microsoft Visual Studio\2022\Enterprise
    ÔÇó Visual Studio Enterprise 2022 version 17.1.32210.238
    ÔÇó Windows 10 SDK version 10.0.22000.0

[ÔêÜ] Android Studio (version 2020.3)
    ÔÇó Android Studio at C:\Program Files\Android\Android Studio
    ÔÇó Flutter plugin can be installed from:
       https://plugins.jetbrains.com/plugin/9212-flutter
    ÔÇó Dart plugin can be installed from:
       https://plugins.jetbrains.com/plugin/6351-dart
    ÔÇó Java version OpenJDK Runtime Environment (build 11.0.10+0-b96-7249189)

[ÔêÜ] VS Code, 64-bit edition (version 1.65.1)
    ÔÇó VS Code at C:\Program Files\Microsoft VS Code
    ÔÇó Flutter extension version 3.27.0

[ÔêÜ] Connected device (4 available)
    ÔÇó Windows (desktop)       ÔÇó windows ÔÇó windows-x64     ÔÇó Microsoft Windows [Version 10.0.22000.556]
    ÔÇó Windows (UWP) (desktop) ÔÇó winuwp  ÔÇó windows-uwp-x64 ÔÇó 
    ÔÇó Chrome (web)            ÔÇó chrome  ÔÇó web-javascript  ÔÇó Google Chrome 99.0.4844.51
    ÔÇó Edge (web)              ÔÇó edge    ÔÇó web-javascript  ÔÇó Microsoft Edge 98.0.1108.56

[ÔêÜ] HTTP Host Availability
    ÔÇó All required HTTP hosts are available

ÔÇó No issues found!
```

Thanks in advance.