Add uv workspace dir command

[mikaylathompson]

Addresses #13636

Prints the path to the workspace root by default, and any of the child packages if requested.

It has a preview flag like workspace metadata, called workspace-dir.

Summary

─> uv workspace dir
/Users/mikayla/code/uv/dev-envs

─> uv workspace dir --package foo-proj
/Users/mikayla/code/uv/dev-envs/foo-proj

─> uv workspace dir --package bar-proj
error: Package `bar-proj` not found in workspace.

Test Plan

Unit tests added.

[zanieb]

I think this should be a separate preview flag so we can stabilize things separately

[zanieb]

(My own doc here is bad, I should fix that)

[codspeed-hq]

CodSpeed Performance Report

Merging #16678 will not alter performance

_{Comparing mikayla/workspace-dir (e249d84) with main (63ab247)}

Summary

✅ 6 untouched

[konstin]

This code compiles without the type cast:

Suggested change

	let dir: &Path = match package_name {
	None => workspace.install_path().as_path(),
	Some(package) => {
	if let Some(p) = workspace.packages().get(&package) {
	p.root().as_path()
	} else {
	bail!("Package `{package}` not found in workspace.")
	}
	}
	};
	let dir = match package_name {
	None => workspace.install_path(),
	Some(package) => {
	if let Some(p) = workspace.packages().get(&package) {
	p.root()
	} else {
	bail!("Package `{package}` not found in workspace.")
	}
	}
	};

[konstin]

nit:

Suggested change

	// Workspace dir output when run with `--package`
	/// Workspace dir output when run with `--package`.