src/vs/workbench/api/common/extHostTypes.ts/NotebookCellData/constructor
class NotebookCellData:	constructor(kind: NotebookCellKind, value: string, languageId: string, mime?: string, outputs?: vscode.NotebookCellOutput[], metadata?: Record<string, any>, executionSummary?: vscode.NotebookCellExecutionSummary) {
		this.kind = kind;
		this.value = value;
		this.languageId = languageId;
		this.mime = mime;
		this.outputs = outputs ?? [];
		this.metadata = metadata;
		this.executionSummary = executionSummary;

		NotebookCellData.validate(this);
	}