Paginator: add scroll event

Unlike `relocate`, which is debounced, a scroll event is useful when you
want to do stuff as soon as it scrolls.

paginator.js

@@ -503,6 +503,7 @@ export class Paginator extends HTMLElement {
         this.#footer = this.#root.getElementById('footer')
 
         this.#observer.observe(this.#container)
+        this.#container.addEventListener('scroll', () => this.dispatchEvent(new Event('scroll')))
         this.#container.addEventListener('scroll', debounce(() => {
             if (this.scrolled) {
                 if (this.#justAnchored) this.#justAnchored = false