feat(docs-infra): add getting started widgets (#26059)

PR Close #26059

aio/src/testing/dom-utils.ts

@@ -0,0 +1,16 @@
+/**
+ * Create a `CustomEvent` (even on browsers where `CustomEvent` is not a constructor).
+ */
+export function createCustomEvent(doc: Document, name: string, detail: any): CustomEvent {
+  const bubbles = false;
+  const cancelable = false;
+
+  // On IE9-11, `CustomEvent` is not a constructor.
+  if (typeof CustomEvent !== 'function') {
+    const event = doc.createEvent('CustomEvent');
+    event.initCustomEvent(name, bubbles, cancelable, detail);
+    return event;
+  }
+
+  return new CustomEvent(name, {bubbles, cancelable, detail});
+}