Repository: flutter
Issue: [flutter_markdown] MarkdownBody.shrinkWrap not taken into account with single child
Labels: package,team-ecosystem,has reproducible steps,P3,p: flutter_markdown,found in release: 3.0,found in release: 3.1,triaged-ecosystem

`MarkdownBody`'s `shrinkWrap` property is not taken into account when the list of children provided by `MarkdownWidget` has only one child.

The reason seems to be that:
1. When there's only one child `MarkdownBody` doesn't wrap it into a `Column`:

https://github.com/flutter/packages/blob/4b2114beb992da0e031c4e9f94e04f6e659e704b/packages/flutter_markdown/lib/src/widget.dart#L443-L453

2. And the inner column that is created by `MarkdownBuilder ` doesn't specify any `mainAxisSize`. 

https://github.com/flutter/packages/blob/4b2114beb992da0e031c4e9f94e04f6e659e704b/packages/flutter_markdown/lib/src/builder.dart#L366-L371

## Steps to Reproduce

```dart
@override
Widget build(BuildContext context) {
  return Stack(
    children: const <Widget>[
      Align(
        alignment: Alignment.bottomCenter,
        child: MarkdownBody(
          data: 'This is a [link](https://flutter.dev/)',
          shrinkWrap: true,
        ),
      ),
    ],
  );
}
```

**Actual results:** The widget takes all the available height.
<img width="359" alt="image" src="https://user-images.githubusercontent.com/6546265/171827092-c00678f8-17eb-4fde-92e1-a31653e886af.png">

**Expected results:** The widget should wrap the markdown content.
<img width="360" alt="image" src="https://user-images.githubusercontent.com/6546265/171827186-39ac4178-6f47-468a-b258-f621c2235462.png">

</details>

<details>
  <summary>Logs</summary>

```
❯ flutter doctor -v
[✓] Flutter (Channel stable, 3.0.1, on macOS 12.4 21F79 darwin-x64, locale en-NL)
    • Flutter version 3.0.1 at /Users/davidmigloz/repos/flutter
    • Upstream repository https://github.com/flutter/flutter.git
    • Framework revision fb57da5f94 (2 weeks ago), 2022-05-19 15:50:29 -0700
    • Engine revision caaafc5604
    • Dart version 2.17.1
    • DevTools version 2.12.2

[✓] Android toolchain - develop for Android devices (Android SDK version 32.1.0-rc1)
    • Android SDK at /Users/davidmigloz/Library/Android/sdk
    • Platform android-32, build-tools 32.1.0-rc1
    • ANDROID_HOME = /Users/davidmigloz/Library/Android/sdk
    • Java binary at: /Users/davidmigloz/Library/Application Support/JetBrains/Toolbox/apps/AndroidStudio/ch-0/212.5712.43.2112.8512546/Android
      Studio.app/Contents/jre/Contents/Home/bin/java
    • Java version OpenJDK Runtime Environment (build 11.0.12+0-b1504.28-7817840)
    • All Android licenses accepted.

[✓] Xcode - develop for iOS and macOS (Xcode 13.4)
    • Xcode at /Applications/Xcode.app/Contents/Developer
    • CocoaPods version 1.11.3

[✓] Chrome - develop for the web
    • Chrome at /Applications/Google Chrome.app/Contents/MacOS/Google Chrome

[✓] Android Studio (version 2021.2)
    • Android Studio at /Users/davidmigloz/Library/Application Support/JetBrains/Toolbox/apps/AndroidStudio/ch-0/212.5712.43.2112.8512546/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 11.0.12+0-b1504.28-7817840)

[✓] Android Studio (version 2021.1)
    • Android Studio at /Users/davidmigloz/Library/Application Support/JetBrains/Toolbox/apps/AndroidStudio/ch-0/211.7628.21.2111.8309675/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 11.0.11+0-b60-7590822)

[✓] IntelliJ IDEA Ultimate Edition (version 2022.1.1)
    • IntelliJ at /Users/davidmigloz/Applications/JetBrains Toolbox/IntelliJ IDEA Ultimate.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

[✓] IntelliJ IDEA Ultimate Edition (version 2022.1.1)
    • IntelliJ at /Users/davidmigloz/Library/Application Support/JetBrains/Toolbox/apps/IDEA-U/ch-0/221.5591.52/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

[✓] IntelliJ IDEA Ultimate Edition (version 2022.1)
    • IntelliJ at /Users/davidmigloz/Library/Application Support/JetBrains/Toolbox/apps/IDEA-U/ch-0/221.5080.210/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

[✓] VS Code (version 1.67.0)
    • VS Code at /Applications/Visual Studio Code.app/Contents
    • Flutter extension version 3.40.0

[✓] Connected device (3 available)
    • Pixel 3 (mobile) • 8ANX0VZ7Q • android-arm64  • Android 12 (API 31)
    • macOS (desktop)  • macos     • darwin-x64     • macOS 12.4 21F79 darwin-x64
    • Chrome (web)     • chrome    • web-javascript • Google Chrome 102.0.5005.61

[✓] HTTP Host Availability
    • All required HTTP hosts are available

• No issues found!
```
</details>