src/vs/workbench/contrib/notebook/browser/contrib/fold/foldingModel.ts/updateFoldingStateAtIndex
export function updateFoldingStateAtIndex(foldingModel: FoldingModel, index: number, collapsed: boolean) {
	const range = foldingModel.regions.findRange(index + 1);
	foldingModel.setCollapsed(range, collapsed);
}