Split `TlsStream` like `TcpStream`

[jmmaloney4]

Tokio allows splitting a TcpStream into a (Owned)ReadHalf / (Owned)WriteHalf via TcpStream::split / TcpStream::into_split, but I don't believe tokio_rustls allows splitting a TlsStream that wraps a TcpStream. Is there a way to do this with the current API that I'm not thinking of? If not, I'd be interested in helping to implement this feature.

The split method in TcpStream above is not the same as tokio::io::split. It supports true simultaneous reads and writes as opposed to just locking around the syscalls.