Fix Regex#inspect with non-literal-compatible options

[straight-shoota]

With this patch Regex#inspect only uses the literal syntax when all option flags can be represented. If options includes additional flags, it uses a more extensive representation based on the constructor form.

I'm not sure if the helper methods #inspect_literal and #inspect_extensive should really be exposed. I can't see any specific use case for calling them directly instead of #inspect. We could make them private and move all documentation to #inspect.

Resolves #14530

[ysbaddaden]

I'd have #inspect_literal and #inspect_extensive be private, and only document that #inspect will usually generate a literal expression but may generate an explicit Regex.new expression when some flags are set; but otherwise 👍