src/vs/base/browser/ui/splitview/splitview.ts/SplitView/getViewCachedVisibleSize
class SplitView:	getViewCachedVisibleSize(index: number): number | undefined {
		if (index < 0 || index >= this.viewItems.length) {
			throw new Error('Index out of bounds');
		}

		const viewItem = this.viewItems[index];
		return viewItem.cachedVisibleSize;
	}