Create closure type; allow async event handlers in props; allow short hand event handlers (#2437)

* create closure type; allow async event handlers in props; allow shorthand event handlers

* test forwarding event handlers with the shorthand syntax

* fix clippy

* fix imports in spawn async doctest

examples/shorthand.rs

@@ -27,12 +27,18 @@ fn app() -> Element {
 }
 
 #[component]
-fn Component(a: i32, b: i32, c: i32, children: Element, onclick: EventHandler) -> Element {
+fn Component(
+    a: i32,
+    b: i32,
+    c: i32,
+    children: Element,
+    onclick: EventHandler<MouseEvent>,
+) -> Element {
     rsx! {
         div { "{a}" }
         div { "{b}" }
         div { "{c}" }
         div { {children} }
-        div { onclick: move |_| onclick.call(()) }
+        div { onclick }
     }
 }