Update Kokkos integration (and switch to default serial on host)

[pgrete]

PR Summary

• Move our existing scattered CMake Kokkos logic to one place
• Removed PARTHENON_DISABLE_OPENMP option (and default to serial for host parallel). OpenMP can be enabled by Kokkos_ENABLE_OPENMP
• Removed logic to enable CUDA lambda (default is on for Kokkos 4)
• Removed explicit disable of deprecated Kokkos 3 code (as we're on 4 now)

Fixes #871
Fixes #897
Fixes #895

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.
• Docs build
• (@lanl.gov employees) Update copyright on changed files

[Yurlungur]

Looks good to me. Love to see a negative line count PR. Doesn't this also resolve #895? ;)

[BenWibking]

Minor comments appended.

[BenWibking]

Is this an issue with the new LLVM-based Intel, or the old Intel compiler, or both?

[pgrete]

Good point.
If it's up to me I'd even remove these this and, if people actually use it, let them move it to a machine specific config.

[BenWibking]

I agree that would be cleaner.

[pgrete]

Any strong feelings here by anyone?

[BenWibking]

Not really.

[pgrete]

Looks good to me. Love to see a negative line count PR. Doesn't this also resolve #895? ;)

Indeed, it does. Linking.

[pgrete]

Can we go ahead and merge?
If there are no additional comments by the end of today, I'll merge tomorrow (unless someone pulls the trigger earlier).

(I just briefly enabled and disabled auto-merge to trigger the full pipeline for testing)