Better handling of extra PCRE2 regex options

[Blacksmoke16]

Discussion

I recently ran into a situation where I needed to use a regex with the Regex::CompileOptions::DOLLAR_ENDONLY option. However after using the Regex.new(String) overload to be able to set the option, the regex caused a PCRE2 stack size limit exceeded error. What ultimately ended up happening was the string being passed to Regex.new was like "[\|]", but was being interpreted as "[|]", changing the semantics of the regex.

The solution was to use %q() such that it was treated similar to a regex literal, which does not have this problem. So the root problem is that if you need to use regex modifiers that are not supported via a regex literal, you have to use the string version.

It would be nice to improve this use case, of which we have a few options that I could think of:

1. Add some additional modifiers to allow using regex literals
2. Add an additional Regex.new overload that accepts a Regex and passes it thru via #source. Would be kind of wasteful given it involves an extra Regex instance, but would allow passing extra options while still being able to use a literal for its ease of use and compile time checks.
3. Possibly just document that %q or similar should be used when using Regex.new(String)
4. TBD