LibWeb: Track if element was created from token with dupe attributes

This is required for CSP to ignore the nonce attribute to prevent
duplicate attributes hijacking the attribute.

See https://w3c.github.io/webappsec-csp/#security-nonce-hijacking

Libraries/LibWeb/HTML/Parser/HTMLToken.cpp

@@ -98,6 +98,7 @@ void HTMLToken::normalize_attributes()
             // This is a duplicate attribute, remove it.
             tag_attributes.remove(i);
             --i;
+            m_had_duplicate_attribute = true;
         }
     }
 }