[css-selectors-level-4] :user-error or :user-invalid?

[kevinSuttle]

Are these 2 different pseudo-selectors?
Both are mentioned here: https://drafts.csswg.org/selectors/#user-pseudos

Also, I wonder if :input-error would be a more appropriate name.

[Loirooriol]

@fantasai I think your commit fixes #1242, not this one.