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/Map.cpp

@@ -22,6 +22,65 @@ Map::~Map()
 {
 }
 
+// 24.1.3.1 Map.prototype.clear ( ), https://tc39.es/ecma262/#sec-map.prototype.clear
+void Map::map_clear()
+{
+    m_keys.clear();
+    m_entries.clear();
+}
+
+// 24.1.3.3 Map.prototype.delete ( key ), https://tc39.es/ecma262/#sec-map.prototype.delete
+bool Map::map_remove(Value const& key)
+{
+    Optional<size_t> index;
+
+    for (auto it = m_keys.begin(); it != m_keys.end(); ++it) {
+        if (ValueTraits::equals(*it, key)) {
+            index = it.key();
+            break;
+        }
+    }
+
+    if (!index.has_value())
+        return false;
+
+    m_keys.remove(*index);
+    m_entries.remove(key);
+    return true;
+}
+
+// 24.1.3.6 Map.prototype.get ( key ), https://tc39.es/ecma262/#sec-map.prototype.get
+Optional<Value> Map::map_get(Value const& key) const
+{
+    if (auto it = m_entries.find(key); it != m_entries.end())
+        return it->value;
+    return {};
+}
+
+// 24.1.3.7 Map.prototype.has ( key ), https://tc39.es/ecma262/#sec-map.prototype.has
+bool Map::map_has(Value const& key) const
+{
+    return m_entries.contains(key);
+}
+
+// 24.1.3.9 Map.prototype.set ( key, value ), https://tc39.es/ecma262/#sec-map.prototype.set
+void Map::map_set(Value const& key, Value value)
+{
+    auto it = m_entries.find(key);
+    if (it != m_entries.end()) {
+        it->value = value;
+    } else {
+        auto index = m_next_insertion_id++;
+        m_keys.insert(index, key);
+        m_entries.set(key, value);
+    }
+}
+
+size_t Map::map_size() const
+{
+    return m_keys.size();
+}
+
 void Map::visit_edges(Cell::Visitor& visitor)
 {
     Base::visit_edges(visitor);