Experiment with call syntax only working for copy types

examples/login_form.rs

@@ -31,7 +31,7 @@ fn app() -> Element {
 
     rsx! {
         h1 { "Login" }
-        form { onsubmit: onsubmit,
+        form { onsubmit,
             input { r#type: "text", id: "username", name: "username" }
             label { "Username" }
             br {}