I spent some time exploring combining all of the TryFindXx and TryMatchXx methods in RegexCompiler / source generator into just a single Scan. It doesn't yet appear to be worth doing, but along the way I tweaked a bunch of things, and am submitting that as a PR separately.

Functional:

• We were throwing NotSupportedException when RegexOptions.NonBacktracking was used in combination with other supported options, but for existing incompatible options we throw ArgumentOutOfRangeException, so we should be doing the same there. We should also do it in the helper where we validate options rather than in the NonBacktracking factory.

Performance:

• Given a pattern like "\w*-", we'll use our literal-after-loop find optimization where we search for the '-' and then walk backwards through the atomic loop looking for where it starts. However, we then record that start-of-loop location as the starting position, and try to match from there, which means we end up then rematching that whole loop again. If the loop is long, that can be non-trivial wasted work. We now store the position after the loop into a field and use that from the matching logic to skip the loop as part of the match.
• We now emit specialized code in Scan for a few common structures, e.g. if the pattern begins with a beginning anchor, we don't need a scan loop at all.

Most everything else is for code readability / maintenance.