Adds reading of omega HorzMesh from mesh iostream

[philipwjones]

Uses an input IOStream to read the input horizontal mesh variables. The same filename is used by Decomp. If the Decomp optional argument for a mesh file is supplied (eg in some unit test drivers), that value overrides the mesh stream filename. All physical mesh fields are defined for IO and are added to a field group HorzMeshIn. Some cleanup of the HorzMesh test driver is included to reduce test output and conform to omega code conventions. User and developer docs have been updated with these changes.

Checklist

• Documentation:
  • Design document has been generated and added to the docs
  • User's Guide has been updated
  • Developer's Guide has been updated
  • Documentation has been built locally and changes look as expected
• Linting
  • Pre-commit run locally
• Building
  • CMake build does not produce any new warnings from changes in this PR
• Testing
  • Add a comment to the PR titled Testing with the following:
    • Which machines CTest unit tests
      have been run on and indicate that are all passing.
    • The Polaris omega_pr test suite
      has passed, using the Polaris e3sm_submodules/Omega baseline
    • Document machine(s), compiler(s), and the build path(s) used for -p for both the baseline (Polaris e3sm_submodules/Omega) and the PR build
    • Indicate "All tests passed" or document failing tests
    • Document testing used to verify the changes including any tests that are added/modified/impacted.
    • Performance related PRs: Please include a relevant PACE experiment link documenting performance before and after.

Fixes #311

[philipwjones]

Passes ctests on Perlmutter (CPU)

[xylar]

Thanks @philipwjones! I'll take a look ASAP.

[xylar]

I'm working on the Polaris side of supporting these changes in E3SM-Project/polaris#527. That's going to need some fixes in Polaris for the horizontal pressure gradient before it can be tested.