src/vs/workbench/api/common/extHostNotebook.ts/ExtHostNotebookController/getIdByEditor
class ExtHostNotebookController:	getIdByEditor(editor: vscode.NotebookEditor): string | undefined {
		for (const [id, candidate] of this._editors) {
			if (candidate.apiEditor === editor) {
				return id;
			}
		}
		return undefined;
	}