LibWeb: Add more fast_is<T> helpers for DOM::Node subclasses

Author: https://github.com/awesomekling
Commit: aecb144df0
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/4395

Libraries/LibWeb/SVG/SVGAElement.h

@@ -31,6 +31,8 @@ private:
     virtual void initialize(JS::Realm&) override;
     virtual void visit_edges(Cell::Visitor&) override;
 
+    virtual bool is_svg_a_element() const override { return true; }
+
     // ^DOM::Element
     virtual void attribute_changed(FlyString const& name, Optional<String> const& old_value, Optional<String> const& value, Optional<FlyString> const& namespace_) override;
     virtual i32 default_tab_index_value() const override;
@@ -39,3 +41,8 @@ private:
 };
 
 }
+
+namespace Web::DOM {
+template<>
+inline bool Node::fast_is<SVG::SVGAElement>() const { return is_svg_a_element(); }
+}