toUrlPath normalizes file paths for URLs; UrlPath type ships

Minor Changes

• #14785 5e6556a Thanks @dario-piotrowicz! - Add toUrlPath and UrlPath exports

  toUrlPath(filePath) converts a file-system path into a URL-safe path by replacing backslashes with forward slashes and rejecting Windows drive-letter prefixes (e.g. C:). UrlPath is the branded string type it returns, letting callers prove at the type level that a string has been normalized for use in URLs.