LibJS: Implement the RegExpStringIterator object

This implementation closely follows the StringIterator object in that
the abstract closure meant to be created in CreateRegExpStringIterator
is instead unrolled into RegExpStringIterator.prototype.next.

Userland/Libraries/LibJS/Runtime/RegExpStringIterator.cpp

@@ -0,0 +1,27 @@
+/*
+ * Copyright (c) 2021, Tim Flynn <trflynn89@pm.me>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <LibJS/Runtime/GlobalObject.h>
+#include <LibJS/Runtime/RegExpStringIterator.h>
+
+namespace JS {
+
+// 22.2.7.1 CreateRegExpStringIterator ( R, S, global, fullUnicode ), https://tc39.es/ecma262/#sec-createregexpstringiterator
+RegExpStringIterator* RegExpStringIterator::create(GlobalObject& global_object, Object& regexp_object, String string, bool global, bool unicode)
+{
+    return global_object.heap().allocate<RegExpStringIterator>(global_object, *global_object.regexp_string_iterator_prototype(), regexp_object, move(string), global, unicode);
+}
+
+RegExpStringIterator::RegExpStringIterator(Object& prototype, Object& regexp_object, String string, bool global, bool unicode)
+    : Object(prototype)
+    , m_regexp_object(regexp_object)
+    , m_string(move(string))
+    , m_global(global)
+    , m_unicode(unicode)
+{
+}
+
+}