src/vs/workbench/api/common/extHostNotebook.ts/ExtHostNotebookController/$saveNotebook
class ExtHostNotebookController:	async $saveNotebook(viewType: string, uri: UriComponents, token: CancellationToken): Promise<boolean> {
		const document = this.getNotebookDocument(URI.revive(uri));
		const { provider } = this._getProviderData(viewType);
		await provider.saveNotebook(document.apiNotebook, token);
		return true;
	}