Fixed #19508 -- Used uri_to_iri.

This is a PR for ticket #19508 for which another PR #2919 was opened by me a few days ago.
This PR implements `uri_to_iri` as per RFC and changes the `PATH_INFO` at the very time when `environ` is being set contrary to the previous one which corrected the received url from `environ`.
When you do `iri.decode(encoding)` you are getting unicode, so effectively you sometime have unicode, sometime bytes. If the caller needs bytes, it can encode in whatever encoding it desires .