LibWeb: Add HTMLTableSectionElement.rows and HTMLTableRowElement.cells

1% progression on ACID3. :^)

Userland/Libraries/LibWeb/HTML/HTMLTableSectionElement.h

@@ -1,5 +1,6 @@
 /*
  * Copyright (c) 2020, the SerenityOS developers.
+ * Copyright (c) 2022, Andreas Kling <kling@serenityos.org>
  *
  * SPDX-License-Identifier: BSD-2-Clause
  */
@@ -16,6 +17,8 @@ public:
 
     HTMLTableSectionElement(DOM::Document&, DOM::QualifiedName);
     virtual ~HTMLTableSectionElement() override;
+
+    NonnullRefPtr<DOM::HTMLCollection> rows() const;
 };
 
 }