src/vs/workbench/contrib/notebook/browser/notebookEditor.ts/NotebookEditor/getViewState
class NotebookEditor:	override getViewState(): INotebookEditorViewState | undefined {
		const input = this.input;
		if (!(input instanceof NotebookEditorInput)) {
			return undefined;
		}

		this._saveEditorViewState(input);
		return this._loadNotebookEditorViewState(input);
	}