src/vs/workbench/contrib/notebook/browser/viewModel/notebookViewModel.ts/NotebookViewModel/getFoldingState
class NotebookViewModel:	getFoldingState(index: number): CellFoldingState {
		if (!this._foldingRanges) {
			return CellFoldingState.None;
		}

		const range = this._foldingRanges.findRange(index + 1);
		const startIndex = this._foldingRanges.getStartLineNumber(range) - 1;

		if (startIndex !== index) {
			return CellFoldingState.None;
		}

		return this._foldingRanges.isCollapsed(range) ? CellFoldingState.Collapsed : CellFoldingState.Expanded;
	}