deprecate werkzeug.urls

[davidism]

Most of the code in werkzeug.urls is a copy of Python 2's urlparse and Python 3's urllib.parse, modified for compatibility between both. Due to the Python 2 to 3 transition for the WSGI spec, it does a ton of str/bytes checks and conversions, even though we only support Python 3 now and could assume str in a lot more places. After #2406 pointed out performance issues, an initial patch to replace our implementation with urllib.parse resulted in a 35% speedup in routing and responses.

The uri_to_iri and iri_to_uri functions will remain, but everything else will be deprecated.