Add TextOutputStream to FileDescriptor?

Would it make sense to add `TextOutputStream` conformance to `FileDescriptor` to support writing something like this:

```swift
print("An error occurred", to: FileDescriptor.standardError)
```

Hmm, I tried doing this:

```swift
print("File exists.", to: &FileDescriptor.standardError) // Cannot pass immutable value as inout argument: 'standardError' is a get-only property

extension
FileDescriptor : TextOutputStream
{
public mutating func write(_ inString: String) {
_ = try? FileDescriptor.standardError.writeAll(inString.utf8)
}
}
```

Perhaps those would be better as `public static` members?

Start with the FileDescriptor API and its standardError member, then review Swift's TextOutputStream requirements. Resolve whether the proposed print(to:) usage and static-member alternative are appropriate; done means an agreed API design with its behavior verified.

Written by the indexing model from the issue text.