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`.
@loic 
Look here: https://github.com/mitsuhiko/werkzeug/blob/master/werkzeug/urls.py#L455
Here also bytes are encoded in `utf-8`, and then decoded in given `charset` kwarg also with an if statement for not `None`