Implement initial-cwd for wasi:cli/environment

[stephenmuss]

This implements initial-cwd for wasi:cli/environment.

My biggest struggle was finding the appropriate places to add tests. Any guidance would be appreciated. Thank you.

Closes #9695

[alexcrichton]

Thanks! I'd recommend adding a test to crates/test-programs/bin/*.rs and there's a small README about the tests in that directory.

[stephenmuss]

I assume I should be able to use something like this in crates/test-programs/bin/*.rs to test

fn main() -> std::io::Result<()> {
    let cwd = std::env::current_dir()?;
    assert_eq!(cwd.to_str(), Some("/tmp"));
    Ok(())
}

and run with -S cwd=/tmp.

Is that understanding correct?

However, I always get Some("/") indicating that I still need to set the path somewhere I've missed, presumably in src/commands/run.rs and src/commands/serve.rs etc.

[alexcrichton]

Ah you'll probably need to use the WASI API directly rather than the standard library because the standard library isn't hooked up to this API yet.