LibRegex: Allow separately parsing patterns and creating Regex objects

Adds a static method to parse a regex pattern and return the result, and
a constructor to accept a parse result. This is to allow LibJS to parse
the pattern string of a RegExpLiteral once and hand off regex objects
any number of times thereafter.

Userland/Libraries/LibRegex/RegexMatcher.h

@@ -80,7 +80,10 @@ public:
     OwnPtr<Matcher<Parser>> matcher { nullptr };
     mutable size_t start_offset { 0 };
 
+    static regex::Parser::Result parse_pattern(StringView pattern, typename ParserTraits<Parser>::OptionsType regex_options = {});
+
     explicit Regex(String pattern, typename ParserTraits<Parser>::OptionsType regex_options = {});
+    Regex(regex::Parser::Result parse_result, String pattern, typename ParserTraits<Parser>::OptionsType regex_options = {});
     ~Regex() = default;
     Regex(Regex&&);
     Regex& operator=(Regex&&);