Move Prelude.Linear.Internal.Simple to Prelude.Linear.Internal

[mboes]

Adjust the imports in other modules as well. However, this begs the
question: why are so many other modules importing the internal
version, instead of Prelude.Linear?

[aspiwack]

I haven't reviewed, yet. But I can answer the question: Prelude.Linear is a prelude for the users of linear-base. It's public facing, and is allowed to depend on anything in linear-base. Prelude.Linear.Internal.{,.Simple} is the prelude of the library.

As it turns out, I believe that the Prelude.Linear is not as late in the dependency hierarchy as its namesake in base. But it's still pretty late.

[mboes]

Makes sense. This should be documented.