Feature request description

When you define a babel.config.js you can return a function, e.g.

https://gist.github.com/gtzilla/a6ae9777a987df1ee1357df51bf9cd61

When parsing this config file, if it a returns a function the function has to be called and provided a stub implementation of that babel api.

See https://babeljs.io/docs/en/config-files#config-function-api