LibWeb: Implement :enabled and :disabled pseudo classes to spec

Previously we only considered an element disabled if it was an <input>
element with the disabled attribute, but there's way more elements that
apply with more nuanced disabled/enabled rules.

Userland/Libraries/LibWeb/HTML/HTMLOptionElement.h

@@ -28,6 +28,8 @@ public:
 
     int index() const;
 
+    bool disabled() const;
+
 private:
     friend class Bindings::OptionConstructor;
     friend class HTMLSelectElement;