Add cancel event (#4476)

* feat: add cancel event

* feat: provide cancel event

* feat: insert cancel event in web

* fix: typo

* feat: propagate implementation of cancel event

* fix merge conflicts / tests

---------

Co-authored-by: Jonathan Kelley <jkelleyrtp@gmail.com>

packages/liveview/src/events.rs

@@ -15,6 +15,14 @@ impl HtmlEventConverter for SerializedHtmlEventConverter {
             .into()
     }
 
+    fn convert_cancel_data(&self, event: &PlatformEventData) -> CancelData {
+        event
+            .downcast::<SerializedCancelData>()
+            .cloned()
+            .unwrap()
+            .into()
+    }
+
     fn convert_clipboard_data(&self, event: &PlatformEventData) -> ClipboardData {
         event
             .downcast::<SerializedClipboardData>()