Unfortunately the built-in components are not written in Freemarker, but in Java, and we don't have a way to convert them into Freemarker. We do have ways to customize aspects of some of these components and in some cases we have Freemarker context objects you can use to re-create the functionality of some of these components. For example, we have a Freemarker object you can use to create a pager (take a look at this KB article: https://lithosphere.lithium.com/t5/Developers-Knowledge-Base/Context-objects-for-custom-components-webuisupport/ta-p/9343). If you post some specific use-cases where you need to customize a particular component, I may be able to help you figure out the best way to customize it.
