Send info about the DocumentType node to the devtools inspector (#36787)

This makes the DOCTYPE tag show up correctly in the inspector.

Before:

![image](https://github.com/user-attachments/assets/fd101337-95ce-45ee-8ac5-ae701109eb94)

After:

![image](https://github.com/user-attachments/assets/4e80f4c0-6ae4-4c53-88ca-614803caa032)


Testing: We don't have devtools tests

Signed-off-by: Simon Wülker <simon.wuelker@arcor.de>

components/script/dom/node.rs

@@ -1283,6 +1283,21 @@ impl Node {
             is_shadow_host,
             shadow_root_mode,
             display,
+            doctype_name: self
+                .downcast::<DocumentType>()
+                .map(DocumentType::name)
+                .cloned()
+                .map(String::from),
+            doctype_public_identifier: self
+                .downcast::<DocumentType>()
+                .map(DocumentType::public_id)
+                .cloned()
+                .map(String::from),
+            doctype_system_identifier: self
+                .downcast::<DocumentType>()
+                .map(DocumentType::system_id)
+                .cloned()
+                .map(String::from),
         }
     }