[Analyzer]: Regex analyzers #68962

There are some common misuses of Regex we could have analyzers for:

• regex.Match(...).Success should just be regex.IsMatch(...) (e.g. https://grep.app/search?q=%5C.Match%28.%2A%29%5C.Success&regexp=true&filter[lang][0]=C%23)
• RegexOptions.CultureInvariant is specified when RegexOptions.IgnoreCase isn't specified and the pattern doesn't contain (?i) (e.g. https://grep.app/search?q=%22%2C%20RegexOptions.CultureInvariant%5C%29&regexp=true&filter[lang][0]=C%23)

We can also flag cases where new Regex APIs would be useful:

• regex.Matches(...).Count should just be regex.Count(...) (e.g. https://grep.app/search?q=%5C.Matches%28.%2A%29%5C.Count&regexp=true&filter[lang][0]=C%23)
• Use of Match but only ever using Index/Length could potentially use the new EnumerateMatches; this one is harder.

And potentially cases where we can easily detect the possibility of catastrophic backtracking and recommend RegexOptions.NonBacktracking.