LibJS: Make Map iterators independent of the underlying hashmap

This implements ordered maps as a pair of an RBTree for key order, and
an underlying unordered hash map for storage.
Fixes (part of) #11004.

Userland/Libraries/LibJS/Runtime/MapIterator.h

@@ -33,7 +33,7 @@ private:
     Map& m_map;
     bool m_done { false };
     Object::PropertyKind m_iteration_kind;
-    OrderedHashMap<Value, Value, ValueTraits>::IteratorType m_iterator;
+    Map::ConstIterator m_iterator;
 };
 
 }