src/vs/editor/standalone/browser/standaloneLanguages.ts/registerDocumentSymbolProvider
export function registerDocumentSymbolProvider(languageSelector: LanguageSelector, provider: languages.DocumentSymbolProvider): IDisposable {
	const languageFeaturesService = StandaloneServices.get(ILanguageFeaturesService);
	return languageFeaturesService.documentSymbolProvider.register(languageSelector, provider);
}