Introduce `OwnedFd` and `BorrowedFd`, and the `AsFd` trait, and implementations of `AsFd`, `From<OwnedFd>` and `From<T> for OwnedFd` for relevant types, along with Windows counterparts for handles and sockets. Tracking issue: - <https://github.com/rust-lang/rust/issues/87074> RFC: - <https://github.com/rust-lang/rfcs/blob/master/text/3128-io-safety.md>