extensions/typescript-language-features/src/languageFeatures/documentSymbol.ts/register
export function register(
	selector: DocumentSelector,
	client: ITypeScriptServiceClient,
	cachedResponse: CachedResponse<Proto.NavTreeResponse>,
) {
	return vscode.languages.registerDocumentSymbolProvider(selector.syntax,
		new TypeScriptDocumentSymbolProvider(client, cachedResponse), { label: 'TypeScript' });
}