LibJS: Add Object.{keys,values,entries}()

Author: https://github.com/mattco98
Commit: 683a0696f3
Pull-request: https://github.com/SerenityOS/serenity/pull/2027
Reviewed-by: https://github.com/awesomekling

Libraries/LibJS/Runtime/ObjectConstructor.h

@@ -48,6 +48,9 @@ private:
     static Value get_own_property_names(Interpreter&);
     static Value get_prototype_of(Interpreter&);
     static Value set_prototype_of(Interpreter&);
+    static Value keys(Interpreter&);
+    static Value values(Interpreter&);
+    static Value entries(Interpreter&);
 };
 
 }