src/vs/workbench/contrib/notebook/browser/notebook.contribution.ts/NotebookContribution/updateCellUndoRedoComparisonKey
class NotebookContribution:	private updateCellUndoRedoComparisonKey(configurationService: IConfigurationService, undoRedoService: IUndoRedoService) {
		const undoRedoPerCell = configurationService.getValue<boolean>(NotebookSetting.undoRedoPerCell);

		if (!undoRedoPerCell) {
			// Add comparison key to map cell => main document
			if (!this._uriComparisonKeyComputer) {
				this._uriComparisonKeyComputer = undoRedoService.registerUriComparisonKeyComputer(CellUri.scheme, {
					getComparisonKey: (uri: URI): string => {
						if (undoRedoPerCell) {
							return uri.toString();
						}
						return NotebookContribution._getCellUndoRedoComparisonKey(uri);
					}
				});
			}
		} else {
			// Dispose comparison key
			this._uriComparisonKeyComputer?.dispose();
			this._uriComparisonKeyComputer = undefined;
		}
	}