LibWeb: Add form associated element categories

Userland/Libraries/LibWeb/HTML/HTMLMeterElement.h

@@ -1,5 +1,6 @@
 /*
  * Copyright (c) 2020, the SerenityOS developers.
+ * Copyright (c) 2022, Luke Wilde <lukew@serenityos.org>
  *
  * SPDX-License-Identifier: BSD-2-Clause
  */
@@ -16,6 +17,10 @@ public:
 
     HTMLMeterElement(DOM::Document&, DOM::QualifiedName);
     virtual ~HTMLMeterElement() override;
+
+    // ^HTMLElement
+    // https://html.spec.whatwg.org/multipage/forms.html#category-label
+    virtual bool is_labelable() const override { return true; }
 };
 
 }