src/vs/workbench/contrib/notebook/browser/viewModel/notebookViewModelImpl.ts/NotebookViewModel/getPreviousVisibleCellIndex
class NotebookViewModel:	getPreviousVisibleCellIndex(index: number) {
		for (let i = this._hiddenRanges.length - 1; i >= 0; i--) {
			const cellRange = this._hiddenRanges[i];
			const foldStart = cellRange.start - 1;
			const foldEnd = cellRange.end;

			if (foldEnd < index) {
				return index;
			}

			if (foldStart <= index) {
				return foldStart;
			}
		}

		return index;
	}