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