WIP : Implementation of MLPoisson::Fsmooth using ParallelFor(MultiFab)

[PaulMullowney]

I had to write wrapper implementations that execute the loops over the box, when compiling for CPU. Also, the compactify method does not compile for GPU. So, the 3D impl with hasHiddenDimension is executed in the old manner. Lastly, the failing HIP tests seem unrelated to this PR.

Summary

Additional background

Checklist

The proposed changes:

• [ ] fix a bug or incorrect behavior in AMReX
• [x] add new capabilities to AMReX
• [ ] changes answers in the test suite to more than roundoff level
• [ ] are likely to significantly affect the results of downstream AMReX users
• [ ] include documentation in the code and/or rst files, if appropriate