Should `FileDescriptor.closeAfter` provide a `FileDescriptor` to the invoked closure?

I've been wanting to write something like

```swift
let foo = try FileDescriptor
.open("my-file", .readOnly)
.closeAfter { fileDescriptor in
/// do stuff with fileDescriptor
}
```

Start at the FileDescriptor.closeAfter API and inspect how it currently invokes its closure. Compare that behavior with the proposed closure receiving a FileDescriptor; done means the requested usage is supported while closeAfter retains its intended close-after behavior.

Written by the indexing model from the issue text.