run() shows garbled text in Windows 10

`run()` and `runAsync()` of `run.dart` module shows garbled text for `flutter doctor` as following

```
[竏咯 Flutter (Channel
```

instead of

```
[√] Flutter (Channel...
```

I can generate this garbled text with encoding "[√]" with `utf8` and then decoding it with `systemEncoding`.

### How to reproduce

Run following in Windows which code point settings is not UTF-8 (`chcp` shows a number other than `65001`):

```dart
run('flutter', arguments: ['doctor'])
```

Note that I found that normal texts are shown with explicitly specifying `utf8` for `RunOptions.stdoutEncoding` and `RunOptions.stderrEncoding`, and `systemEncoding` is properly set to ANSI encoding of my environment.

### Workaround

We can avoid this issue with passing `RunOptions(stdoutEncoding: utf8, stderrEncoding: utf8, ...)` for `run()` and `runAsync()`.

### Environments

* grinder: 0.9.0
* Windows: Windows10 21H1 (build 19043.1237)
* Result of `chcp`: 932