Repository: flutter
Issue: [web] "Enable accessibility" read by screen reader even when accessibility is auto-enabled
Labels: a: accessibility,platform-web,has reproducible steps,P2,found in release: 2.10,found in release: 2.11,customer: troy,team-web,triaged-web

With accessibility auto-enabled, a screen reader should _never_ read "Enable accessibility" as it suggests to our visitors that accessibility is something that we consider optional.

## Steps to Reproduce

1. Create an app with [accessibility auto-enabled](https://docs.flutter.dev/development/accessibility-and-localization/accessibility#screen-readers) (see "Code sample" for an example).
```dart
RendererBinding.instance!.setSemanticsEnabled(true);
```
2. Execute `flutter run -d chrome`. (This issue is reproducible with both the `html` and `canvaskit` renderers.)
3. View the app with a screen reader (VoiceOver is used in the attached video).

**Expected results:**

Since accessibility is auto-enabled, the screen reader should _not_ read "Enable accessibility".

**Actual results:**

The screen reader reads "Enable accessibility". If you don't notice the issue, try reloading. This appears to be a race condition between when the screen reader starts reading the page and when the `flt-semantics-placeholder` element is removed from the DOM.

<details>
<summary>Code sample</summary>

```dart
import 'package:flutter/material.dart';
import 'package:flutter/rendering.dart';              

void main() {
  WidgetsFlutterBinding.ensureInitialized();

  // Auto-enable accessibility for our Blind and Low Vision customers (see
  // https://docs.flutter.dev/development/accessibility-and-localization/accessibility#screen-readers).
  RendererBinding.instance!.setSemanticsEnabled(true);

  runApp(const MyApp());
}

class MyApp extends StatelessWidget {
  const MyApp({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Title(
        title: 'My App',
        color: Colors.black,
        child: const Scaffold(
          body: Center(
            child: MyWidget(),
          ),
        ),
      )
    );
  }
}

class MyWidget extends StatelessWidget {
  const MyWidget({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return TextButton(
      onPressed: () => {},
      child: const Text('Button'),
    );
  }
}
```

</details>

<details>
  <summary>Logs</summary>

```
[✓] Flutter (Channel stable, 2.10.0, on macOS 11.6.2 20G314 darwin-x64, locale en-US)
    • Flutter version 2.10.0 at /Users/vsomayaji/Dev/flutter
    • Upstream repository https://github.com/flutter/flutter.git
    • Framework revision 5f105a6ca7 (8 days ago), 2022-02-01 14:15:42 -0800
    • Engine revision 776efd2034
    • Dart version 2.16.0
    • DevTools version 2.9.2

[✓] Android toolchain - develop for Android devices (Android SDK version 30.0.3)
    • Android SDK at /Users/vsomayaji/Library/Android/sdk
    • Platform android-31, build-tools 30.0.3
    • Java binary at: /Applications/Android Studio.app/Contents/jre/Contents/Home/bin/java
    • Java version OpenJDK Runtime Environment (build 11.0.10+0-b96-7281165)
    • All Android licenses accepted.

[✓] Xcode - develop for iOS and macOS (Xcode 13.2.1)
    • Xcode at /Applications/Xcode.app/Contents/Developer
    • CocoaPods version 1.11.2

[✓] Chrome - develop for the web
    • Chrome at /Applications/Google Chrome.app/Contents/MacOS/Google Chrome

[✓] Android Studio (version 2020.3)
    • Android Studio at /Applications/Android Studio.app/Contents
    • Flutter plugin can be installed from:
      🔨 https://plugins.jetbrains.com/plugin/9212-flutter
    • Dart plugin can be installed from:
      🔨 https://plugins.jetbrains.com/plugin/6351-dart
    • Java version OpenJDK Runtime Environment (build 11.0.10+0-b96-7281165)

[✓] IntelliJ IDEA Ultimate Edition (version 2021.1.2)
    • IntelliJ at /Applications/IntelliJ IDEA.app
    • Flutter plugin can be installed from:
      🔨 https://plugins.jetbrains.com/plugin/9212-flutter
    • Dart plugin can be installed from:
      🔨 https://plugins.jetbrains.com/plugin/6351-dart

[✓] Connected device (1 available)
    • Chrome (web) • chrome • web-javascript • Google Chrome 98.0.4758.80

[✓] HTTP Host Availability
    • All required HTTP hosts are available

• No issues found!
```

</details>

https://user-images.githubusercontent.com/1007109/153303350-34b6e1e4-f7f4-41ec-a65d-c7b4816d707a.mov