LibWeb: Add HTML elements to factories, add missing tags and attributes

This is mostly to get the grunt work of the way. This is split up into
multiple commits to hopefully make it more manageable to review.

Note that these are not full implementations, and the bindings mostly
get the low hanging fruit.

Also implements some attributes that I kept out because they had
dashes in them. Therefore, this closes #2905.

Libraries/LibWeb/DOM/Node.h

@@ -95,6 +95,7 @@ public:
     String child_text_content() const;
 
     virtual bool is_html_element() const { return false; }
+    virtual bool is_unknown_html_element() const { return false; }
 
     const Node* root() const;
     bool is_connected() const;