Use HTML's parse a URL for xml-stylesheet

[annevk]

If you look at https://wpt.fyi/results/html/infrastructure/urls/resolving-urls/query-encoding/windows-1251.html%3Finclude%3Dxml and surrounding tests it's pretty clear that user agents are aligned on not always using the UTF-8 URL encoding for <?xml-stylesheet?> despite that making a lot of sense.

At this point maybe we should admit defeat and update the specification and test expectations.

Thoughts?

cc @zcorpan @chrishtr

[zcorpan]

Agreed.