AnyCTO with arbitrary number of functions

[AlexanderSinn]

Summary

This PR extends AnyCTO to support an arbitrary number of optimized functions. Some constructs such as PrefixSum need multiple functions that may need to be optimized. It is also possible to provide no GPU function, in which case the compile time parameters will be directly given to the CPU function.

Additional background

Checklist

The proposed changes:

• fix a bug or incorrect behavior in AMReX
• 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