src/vs/workbench/api/common/extHostTypes.ts/NotebookEdit/isNotebookCellEdit
class NotebookEdit:	static isNotebookCellEdit(thing: any): thing is NotebookEdit {
		if (thing instanceof NotebookEdit) {
			return true;
		}
		if (!thing) {
			return false;
		}
		return NotebookRange.isNotebookRange((<NotebookEdit>thing))
			&& Array.isArray((<NotebookEdit>thing).newCells);
	}