src/vs/workbench/api/common/extHostNotebookDocument.ts/ExtHostNotebookDocument/constructor
class ExtHostNotebookDocument:	constructor(
		private readonly _proxy: extHostProtocol.MainThreadNotebookDocumentsShape,
		private readonly _textDocumentsAndEditors: ExtHostDocumentsAndEditors,
		private readonly _textDocuments: ExtHostDocuments,
		readonly uri: URI,
		data: extHostProtocol.INotebookModelAddedData
	) {
		this._notebookType = data.viewType;
		this._metadata = Object.freeze(data.metadata ?? Object.create(null));
		this._spliceNotebookCells([[0, 0, data.cells]], true /* init -> no event*/, undefined);
		this._versionId = data.versionId;
	}