Refactor WebEventExt (#2707)

* Create WebEventExt::try_as_web_event and refactor
* Inline and adjust error message
* Inline downcast methods

packages/html/src/events/pointer.rs

@@ -17,6 +17,7 @@ impl PointerData {
     }
 
     /// Downcast this event to a concrete event type
+    #[inline(always)]
     pub fn downcast<T: 'static>(&self) -> Option<&T> {
         self.inner.as_any().downcast_ref::<T>()
     }