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`.
Hmm.. I understand that. There is a question: What did you wanted this kwarg to do actually...I mean give a decoded string or else?
`iri` gets correct url in bytes.
As far as I know those bytes are utf-8 encoded, so I am a little confused here..what should I be doing??