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