Split out attr() URL parse error WPT tests from attr-all-types.html & attr-security.html. (#62325)

See change proposal [1] and the corresponding spec issue [2].

[1]: https://github.com/web-platform-tests/interop/issues/1303
[2]: https://github.com/w3c/csswg-drafts/issues/13946

Two subtests merge into one, because they test the same thing; that is,
set an unregistered variable with `attr(data-foo, <url>)` and verify
that it fails to parse.

Differential Revision: https://phabricator.services.mozilla.com/D321878

bugzilla-url: https://bugzilla.mozilla.org/show_bug.cgi?id=2067149
gecko-commit: 96c3ed3a6b0935f4a9fe0c3a4950dc05a5dcf695
gecko-commit-git: 016e58dbe0734edfb98a251d634cb4cb5ab53aec
gecko-reviewers: firefox-style-system-reviewers, emilio