feat: no-empty-character-class support v flag

[mdjermanovic]

Prerequisites checklist

• I have read the contributing guidelines.

What is the purpose of this pull request? (put an "X" next to an item)

[ ] Documentation update
[ ] Bug fix (template)
[ ] New rule (template)
[x] Changes an existing rule (template)
[ ] Add autofix to a rule
[ ] Add a CLI option
[ ] Add something to the core
[ ] Other, please explain:

Refs #17223

Updates no-empty-character-class to report nested empty character classes.

What changes did you make? (Give an overview)

Before this change, this rule was reporting some but not all empty nested character classes, depending on how its own parsing happened to work with the new syntax. Since the syntax becomes too complicated for analyzing patterns with a regex, I switched the rule to use regexpp. For performance reasons, I also added a quick search for [] to exit early and avoid parsing.

Is there anything you'd like reviewers to focus on?

Does reporting nested character classes makes sense for this rule? I don't think there's a case where an empty nested character class can be useful.

Note: Allowing empty [^] is existing behavior, it was just undocumented and untested.

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[snitin315]

LGTM, thanks! Will leave it open for others to review

[nzakas]

LGTM. And yes, I think it makes sense for this rule to check for nested empty character classes.