SE-0351: Regex Builder DSL

[rxwei (Richard Wei)]

@dlbuckley

if you use the DSL to build a regex could you output the raw regex from it?

I think it's a useful future direction! However, I wanted to clarify two things:

• Regex's underlying representation is not the textual regex, but a general-purpose pattern matching program (for efficiency). So obtaining a textual regex from Regex would be a conversion.
• Not every Regex built with regex builder can be converted to a textual regex. Regex builder supports arbitrary types that conform to the RegexComponent protocol, including CustomMatchingRegexComponent (pitched in regex-powered string processing algorithms) which can be implemented with arbitrary code. If a Regex contains a CustomMatchingRegexComponent, it cannot be converted to a textual regex.