Enable zero-sized Type in TypeMultiplier

[AlexanderSinn]

Summary

In C++ it is not allowed to make a zero-sized array type like int[0] so a more verbose way using amrex::TypeArray<int, 0> needs to be used. Additionally, std::declval is now used instead of Types{}.

Additional background

Zero-variants in BLAST-ImpactX/impactx#1104

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

[ax3l]

Oh yay!