Introduce BuilderInternals abstraction layer

[fgimenez]

NodeTypeWithComponents adds adapters as part of the build process; most of this might become simpler if we could combine generics into an additional trait. Instead of enforcing specific types in node builder fields we want to introduce an additional abstraction layer in the form of a BuilderInternals trait that represents the node builder state.

The builder operates on the adapter types. We can try to operate on traits and generics entirely, remove the fields with the adapter types and use instead a single adapter that implements the internal helper trait BuilderInternals.

• trait BuilderInternals with associated types
• BuilderComponentsAdapter as concrete struct
• changes in NodeTypeWithComponents to have a single field BuilderComponentsAdapter