[CL-834] Use intersection observer to determine if content scrolls (#16099)

* use intersection observer to fix dynamic content load issue

* set up mock intersection observer

* Create reusable hasScrollable content util

* return null from resize to fix type error

* remove Observer mock

* return observable

* refactor util and remove resize

* use async pipe for observable in template

* remove comment left in error

libs/components/src/utils/dom-observables.ts

@@ -0,0 +1,17 @@
+import { Observable } from "rxjs";
+
+/** IntersectionObserver Observable */
+export const intersectionObserver$ = (
+  target: Element,
+  init: IntersectionObserverInit,
+): Observable<IntersectionObserverEntry> => {
+  return new Observable((sub) => {
+    const io = new IntersectionObserver((entries) => {
+      for (const e of entries) {
+        sub.next(e);
+      }
+    }, init);
+    io.observe(target);
+    return () => io.disconnect();
+  });
+};