Normalize RFC 4007 delimiter for IPv6 Zone IDs

[sethmlarson]

RFC 4007 allows % as the delimiter for IPv6 zone IDs whereas RFC 6874 specifically uses %25 to comply with the host component rules in RFC 3986. We need to assume 6874 and normalize 4007 -> 6874. See discussion in urllib3/urllib3#1531.

[sigmavirus24]

I think we want to support them in-so-much-as being able to normalize to the correct syntax and such, right? I think I'm worried about the "We need to ... accept ... 4007" bit because I'm not sure what acceptance means today

[sethmlarson]

Sure, I'll change the problem statement to normalize. We don't want to validate these URLs as 3986 compliant.

[sethmlarson]

Discovered an issue with where we're doing the IPv6 Zone ID validation that makes normalization not work as we want it to.

parse_result = rfc3986.ParseResult.from_string("http://[::1%eth0]", lazy_normalize=False)

# This should not error but does currently in master.
rfc3986.validator.Validator().check_validity_of('host').validate(parse_result.referece)

[sigmavirus24]

What is "lazy_normalize"?

[sethmlarson]

Controls whether the internal uri reference is normalized after parsing. I think what's happening is the authority is getting detected as invalid and is being stripped off before the normalizer gets to see the host to normalize.