Implements#98791 (comment)

If we have a set of values like["ab", "c!"], we can expand it to["ab", "Ab" "aB", "AB", "c!", "C!"] and switch to case-sensitive searching.
As long as we're making use of buckets that would otherwise have been empty, this is going to be an improvement as the prefix search loop is a bit simpler due to not needing to deal with casing. In the below benchmark, it means eliminatingthis step from the loop.

This optimization is a bit niche (unlikely to be applicable often), but it's really cheap to check whether it could apply, and can help cases with many non-letter characters in their prefixes.

publicclassIgnoreCaseToOrdinal{privatestaticreadonlySearchValues<string>s_values=SearchValues.Create(["ab","c!"],StringComparison.OrdinalIgnoreCase);privatereadonlystring_text=new('\n',1000);[Benchmark]publicintIndexOfAny()=>_text.AsSpan().IndexOfAny(s_values);}