src/vs/workbench/api/common/extHostTypes.ts/NotebookCellOutputItem/isNotebookCellOutputItem
class NotebookCellOutputItem:	static isNotebookCellOutputItem(obj: unknown): obj is vscode.NotebookCellOutputItem {
		if (obj instanceof NotebookCellOutputItem) {
			return true;
		}
		if (!obj) {
			return false;
		}
		return typeof (<vscode.NotebookCellOutputItem>obj).mime === 'string'
			&& (<vscode.NotebookCellOutputItem>obj).data instanceof Uint8Array;
	}