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