Currently, renderers implemented in-language must include extensive logic to emulate how built-in renderers use converters. With #1333 this gap would grow even further.

It would be nice provide methods that in-language renderers can call to perform the same function.

Maybe something like this

abstract class BaseValueRenderer {
  // ...

  external function convertValue(value: Any): Any

  // and for annotation converter support
  external function convertProperty(name: String, value: Any): Pair<String, Any> | RenderDirective

  // ...
}