Make a global variable for whether simulation is a restart

[brryan]

PR Summary

It would be convenient downstream to be able to access is_restart as a global variable (when determining whether input parameters are set or not set appropriately only during initialization) -- right now whether we're restarted is hard to access outside driver classes or ParthenonManager. This PR adds Globals::is_restart set at the same time as Globals::my_rank.

Along the way I also added a soft_equiv function to utils/robust.hpp which would also be useful downstream.

I also renamed tst/unit/kokkos_abstraction.cpp -> tst/unit/test_kokkos_abstraction.cpp for consistency. Stop me if there's a reason to not do that.

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
• Change is breaking (API, behavior, ...)
  • Change is additionally added to CHANGELOG.md in the breaking section
  • PR is marked as breaking
  • Short summary API changes at the top of the PR (plus optionally with an automated update/fix script)
• CI has been triggered on Darwin for performance regression tests.
• Docs build
• (@lanl.gov employees) Update copyright on changed files

[Yurlungur]

LGTM