src/vs/workbench/contrib/notebook/browser/notebookEditor.ts/NotebookEditor/getSelection
class NotebookEditor:	getSelection(): IEditorPaneSelection | undefined {
		if (this._widget.value) {
			const cellUri = this._widget.value.getActiveCell()?.uri;
			if (cellUri) {
				return new NotebookEditorSelection(cellUri);
			}
		}

		return undefined;
	}