Use throttler to limit the number of updates

Using throttler over debouncer proposed in jupyterlab#15109 because
debouncer would not show cells progressively during resize
until user has stopped resizing.

packages/ui-components/src/components/windowedlist.ts

@@ -16,6 +16,7 @@ import { ArrayExt } from '@lumino/algorithm';
 import { PromiseDelegate } from '@lumino/coreutils';
 import { IDisposable } from '@lumino/disposable';
 import { Message, MessageLoop } from '@lumino/messaging';
+import { Throttler } from '@lumino/polling';
 import { ISignal, Signal } from '@lumino/signaling';
 import { PanelLayout, Widget } from '@lumino/widgets';
 
@@ -688,6 +689,7 @@ export class WindowedList<
     this._scrollToItem = null;
     this._scrollRepaint = null;
     this._scrollUpdateWasRequested = false;
+    this._updater = new Throttler(() => this.update(), 50);
     this._resizeObserver = null;
 
     this._viewModel.stateChanged.connect(this.onStateChanged, this);
@@ -727,6 +729,14 @@ export class WindowedList<
     return this._viewModel;
   }
 
+  /**
+   * Dispose the windowed list.
+   */
+  dispose(): void {
+    this._updater.dispose();
+    super.dispose();
+  }
+
   /**
    * Callback on event.
    *
@@ -884,7 +894,7 @@ export class WindowedList<
     this.viewModel.height =
       msg.height >= 0 ? msg.height : this.node.getBoundingClientRect().height;
     if (this.viewModel.height !== previousHeight) {
-      this.update();
+      void this._updater.invoke();
     }
     super.onResize(msg);
   }
@@ -1118,6 +1128,7 @@ export class WindowedList<
   private _scrollRepaint: number | null;
   private _scrollToItem: [number, WindowedList.ScrollToAlign] | null;
   private _scrollUpdateWasRequested: boolean;
+  private _updater: Throttler;
 }
 
 /**