feat: support internal path in exports field

[izaera]

This is needed for LPS-176053 implementation because we need to create a @liferay/api module that will export all our public APIs and we have decided (as a start) to modularize the API with internal paths, like this:

• @liferay/api: will contain general APIs like the ones we provided now in the Liferay object
• @liferay/api/data-set: will contains data-set APIs like the custom cell renderer we are investigating in LPS-176053
• ...

If this doesn't break the current portal build (it shouldn't) I'll release a new version so that those wanting to do it can run the PoC locally.

[izaera]

Since this is green and I need to release a new version to test, I'll merge it.