[wishlist] portable way to pipe one command’s stdout to another’s stdin

[nagisa]

Currently piping output between two commands involves going through raw handles and filedescriptors which requires #[cfg]d code and imports or spawning a thread and juggling data between two streams manually.

Ideally the API would be as simple as this:

let pipe = Stdio::interprocess_pipe();
let cmd1 = ….stdout(pipe.clone()).spawn();
let cmd2 = ....stdin(pipe).status();

or something along the lines.

[alexcrichton]

Added in #42133