Function try_rewrite_target 

fn try_rewrite_target(
    target: &str,
    base_dir: &Path,
    root: &Path,
    src_to_url: &HashMap<(String, String), String>,
    repo: Option<&str>,
    commit: Option<&str>,
) -> Option<String>

Resolve target against base_dir and return either the matching vocs page URL (.sol) or a {repo}/blob/{commit}/... URL for any other relative path under root.