GH-127090: Fix `urllib.response.addinfourl.url` value for opened `file:` URIs (#127091)

The canonical `file:` URL (as generated by `pathname2url()`) is now used as the `url` attribute of the returned `addinfourl` object. The `addinfourl.url` attribute reflects the resolved URL for both `file:` or `http[s]:` URLs now.