WIP: Fix single precision configuration

[pgrete]

PR Summary

In theory we already supported single precision. In practice, it didn't work (not even compilation).

Todos:

• [ ] Add test coverage for single prec
• [ ] Check that all time/timing related parameters are Real64
• Check that all reductions, reduce to Real64
  • [ ] kernels
  • [ ] MPI
• [ ] check use of Real override in unit tests
• Discuss
  • [ ] (fixed) type for particles positions
  • [ ] (fixed) type for coordinates

PR Checklist

• [ ] Code passes cpplint
• [ ] New features are documented.
• [ ] Adds a test for any bugs fixed. Adds tests for new features.
• [ ] Code is formatted
• [ ] Changes are summarized in CHANGELOG.md
• [ ] CI has been triggered on Darwin for performance regression tests.
• [ ] (@lanl.gov employees) Update copyright on changed files

[pgrete]

@brryan I encountered some interesting behavior for particles when I tried to compile in single precision. Most of the position ("x", "y", "z") related function were hard-coded to double, which I understand. However, the Views themselves were Real resulting in a mismatch when trying to get the data because the map would return Real where doubles are expected in further processing. Hardcoding the positions to double/Real64 could be an option, but it would require to add just another map next to int and Real. What's your take on this?

[Yurlungur]

@pgrete @brryan what's the status here?

[pgrete]

Probably still not working and needs fixing.