[FIX] events: correctly call handlers in iframes

Previously, event handlers would not work when an app was mounted in an
iframe, this is caused by a guard in the event handler that checks that
the target element is still in the document, but it doesn't check
against the correct document in the case of an iframe.

This commit changes the check to check against the target's
ownerDocument.

src/runtime/blockdom/events.ts

@@ -27,8 +27,8 @@ function createElementHandler(evName: string, capture: boolean = false): EventHa
   }
 
   function listener(ev: Event) {
-    const currentTarget = ev.currentTarget;
-    if (!currentTarget || !document.contains(currentTarget as HTMLElement)) return;
+    const currentTarget = ev.currentTarget as HTMLElement;
+    if (!currentTarget || !currentTarget.ownerDocument.contains(currentTarget)) return;
     const data = (currentTarget as any)[eventKey];
     if (!data) return;
     config.mainEventHandler(data, ev, currentTarget);