fix: memory leak in notebook editor widget

[SimonSiefke]

Fixes a memory leak in notebookEditorWidget.

Details

In notebookEditorWidget, when the list height changes, the scrollheight is updated. And each time the list changes height, a new disposable is added to this._localStore, making the number of disposables grow by one each time the list content height changes:

this._localStore.add(this._list.onDidChangeContentHeight(() => {
		this._localStore.add(DOM.scheduleAtNextAnimationFrame(DOM.getWindow(this.getDomNode()), () => {
			hasPendingChangeContentHeight = false;
			this._updateScrollHeight();
		}, 100));
}));

Change

The change uses a MutableDisposable so that there can be at most one disposable for the animation frame registered

const renderScrollHeightDisposable = this._localStore.add(new MutableDisposable());

this._localStore.add(this._list.onDidChangeContentHeight(() => {
		renderScrollHeightDisposable.value = DOM.scheduleAtNextAnimationFrame(DOM.getWindow(this.getDomNode()), () => {
			hasPendingChangeContentHeight = false;
			this._updateScrollHeight();
		}, 100);
}));

Before

When executing a notebook cell 37, the number of functions in AnimationFrameQueueItem and NotebookEditorWidget seems to grow by one each time:

After

When executing a notebook cell 37, the number of AnimationFrameQueueItem stays constant (only some things link UndoGroup and StackOperations grow, which seems fine):