LibJS: Add String.raw

Author: https://github.com/mattco98
Commit: ab652fa1ee
Pull-request: https://github.com/SerenityOS/serenity/pull/2140
Reviewed-by: https://github.com/awesomekling

Libraries/LibJS/Runtime/StringConstructor.h

@@ -41,6 +41,8 @@ public:
 private:
     virtual bool has_constructor() const override { return true; }
     virtual const char* class_name() const override { return "StringConstructor"; }
+
+    static Value raw(Interpreter&);
 };
 
 }