src/vs/editor/standalone/browser/standaloneEditor.ts/onDidChangeModelLanguage
export function onDidChangeModelLanguage(listener: (e: { readonly model: ITextModel; readonly oldLanguage: string }) => void): IDisposable {
	const modelService = StandaloneServices.get(IModelService);
	return modelService.onModelLanguageChanged((e) => {
		listener({
			model: e.model,
			oldLanguage: e.oldLanguageId
		});
	});
}