src/vs/workbench/contrib/notebook/common/model/notebookTextModel.ts/NotebookTextModel/_appendNotebookCellOutputItems
class NotebookTextModel:	private _appendNotebookCellOutputItems(cell: NotebookCellTextModel, outputId: string, items: IOutputItemDto[]) {
		const outputIndex = cell.outputs.findIndex(output => output.outputId === outputId);

		if (outputIndex < 0) {
			return;
		}

		const output = cell.outputs[outputIndex];
		output.appendData(items);
		this._eventEmitter.emit({
			kind: NotebookCellsChangeType.OutputItem,
			index: this._cells.indexOf(cell),
			outputId: output.outputId,
			outputItems: items,
			append: true,
			transient: this.transientOptions.transientOutputs
		}, true);
	}