LibWeb: Allow focusable for the first summary child of a detail element

Author: https://github.com/lpas
Commit: bd56fdc57b
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/6780
Reviewed-by: https://github.com/gmta ✅

Libraries/LibWeb/HTML/HTMLSummaryElement.h

@@ -21,10 +21,11 @@ public:
     // https://www.w3.org/TR/html-aria/#el-details
     virtual Optional<ARIA::Role> default_role() const override { return ARIA::Role::button; }
 
-    bool is_summary_for_its_parent_details();
+    bool is_summary_for_its_parent_details() const;
 
     virtual bool has_activation_behavior() const override;
     virtual void activation_behavior(DOM::Event const&) override;
+    virtual bool is_focusable() const override;
 
 private:
     HTMLSummaryElement(DOM::Document&, DOM::QualifiedName);