LibWeb: Implement more table support in the new HTML parser

This is enough to parse the Google front page! (Note: I did have to
hack the tokenizer while parsing Google, in order to avoid named
character references screwing everything up. We'll fix that too soon
enough!)

Libraries/LibWeb/Parser/ListOfActiveFormattingElements.h

@@ -56,6 +56,8 @@ public:
 
     Element* last_element_with_tag_name_before_marker(const FlyString& tag_name);
 
+    void clear_up_to_the_last_marker();
+
 private:
     Vector<Entry> m_entries;
 };