Support wasi-cli (stdin, stdout)

[Timmmm]

Currently you can't use Tokio's stdin/stdout support (the io-std feature flag) on WASI. But WASI does support that in wasi-cli. I believe it is supported by Node now.

This would be immensely useful for distributing Rust LSP servers as WASI modules, so I don't have to cross compile for at least 4 targets. The best Rust LSP crate I've found is tower-lsp which uses Tokio, but the easiest way to communicate with the language server client (i.e. VSCode) is over stdin/stdout.

See also #4827