src/vs/workbench/contrib/notebook/browser/notebookServiceImpl.ts/NotebookOutputRendererInfoStore/setPreferred
class NotebookOutputRendererInfoStore:	setPreferred(mimeType: string, rendererId: string) {
		this.preferredMimetype.getValue()[mimeType] = rendererId;
		this.preferredMimetypeMemento.saveMemento();
	}