public static <T> ExtensionLoader<T> getExtensionLoader(Class<T> clazz) {
        return getExtensionLoader(clazz, null);
    }
Get extension loader by extensible class without listener

@param clazz Extensible class
@param <T>   Class
@return ExtensionLoader of this class
core/api/src/main/java/com/alipay/sofa/rpc/ext/ExtensionLoaderFactory.java