LibWeb: Add form associated element categories

Author: https://github.com/Lubrsi
Commit: 432d496ed6
Pull-request: https://github.com/SerenityOS/serenity/pull/12837

Userland/Libraries/LibWeb/HTML/HTMLProgressElement.h

@@ -27,6 +27,10 @@ public:
 
     double position() const;
 
+    // ^HTMLElement
+    // https://html.spec.whatwg.org/multipage/forms.html#category-label
+    virtual bool is_labelable() const override { return true; }
+
 private:
     bool is_determinate() const { return has_attribute(HTML::AttributeNames::value); }
 };