LibWeb: Support fast_is<T>() for table, table sections, rows and cells

3.2x speed-up on WebKit/PerformanceTests/DOM/GridSort.html

Userland/Libraries/LibWeb/HTML/HTMLTableSectionElement.h

@@ -30,6 +30,8 @@ public:
 private:
     HTMLTableSectionElement(DOM::Document&, DOM::QualifiedName);
 
+    virtual bool is_html_table_section_element() const override { return true; }
+
     virtual void initialize(JS::Realm&) override;
     virtual void visit_edges(Cell::Visitor&) override;
 
@@ -37,3 +39,8 @@ private:
 };
 
 }
+
+namespace Web::DOM {
+template<>
+inline bool Node::fast_is<HTML::HTMLTableSectionElement>() const { return is_html_table_section_element(); }
+}