Issue 34360: urllib.parse doesn't fully comply to RFC 3986

Since bpo-29651, the urllib.parse docs say:

> Unmatched square brackets in the netloc attribute will raise a ValueError.

However, when there are at least one [ and ], but they don't match, there's somewhat inconsistent behavior:

>>> urllib.parse.urlparse('http://[::1]]').hostname
'::1'
>>> urllib.parse.urlparse('http://[[::1]').hostname
'[::1'