src/vs/workbench/api/common/extHostNotebookKernels.ts/ExtHostNotebookKernels/getIdByController
class ExtHostNotebookKernels:	getIdByController(controller: vscode.NotebookController) {
		for (const [_, candidate] of this._kernelData) {
			if (candidate.controller === controller) {
				return createKernelId(candidate.extensionId, controller.id);
			}
		}
		return null;
	}