LibJS: Add an Iterator constructor and object

The Iterator object cannot be constructed directly but can be subclassed
or created with `Iterator.from` (not implemented here).

Userland/Libraries/LibJS/Runtime/Iterator.cpp

@@ -0,0 +1,27 @@
+/*
+ * Copyright (c) 2023, Tim Flynn <trflynn89@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <LibJS/Runtime/Iterator.h>
+
+namespace JS {
+
+ThrowCompletionOr<NonnullGCPtr<Iterator>> Iterator::create(Realm& realm, Object& prototype, IteratorRecord iterated)
+{
+    return MUST_OR_THROW_OOM(realm.heap().allocate<Iterator>(realm, prototype, move(iterated)));
+}
+
+Iterator::Iterator(Object& prototype, IteratorRecord iterated)
+    : Object(ConstructWithPrototypeTag::Tag, prototype)
+    , m_iterated(move(iterated))
+{
+}
+
+Iterator::Iterator(Object& prototype)
+    : Iterator(prototype, {})
+{
+}
+
+}