Extend manufactured solution to del2 and del4

[cbegeman]

This PR adds manufactured solution tests for del2 and del4 and renames the existing case to default. Both del2 and del4 tests depend on the corresponding source terms being added to the model. These terms are added to MPAS-Ocean here E3SM-Ocean-Discussion/E3SM#110. All tests depend on E3SM-Ocean-Discussion/E3SM#55 to achieve expected convergence.

Several parameter combinations of wavelength, viscosity, and horizontal resolution were tested and no combination was found to exercise del4 over a factor of 8 in resolution. Thus, del4 is included here with the same parameter options as del2 and default but it does not alter the convergence rate.

Checklist

• User's Guide has been updated
• Documentation has been built locally and changes look as expected
• Testing comment in the PR documents testing used to verify the changes
• New tests have been added to a test suite -- will not be added until Evaluate time dependent tendencies at correct RK4 stage time value E3SM-Ocean-Discussion/E3SM#55 is merged

[cbegeman]

Testing

MPAS-Ocean tests have been run with E3SM-Ocean-Discussion/E3SM#110 and E3SM-Ocean-Discussion/E3SM#55.
Default convergence:

Del2 convergence:

Omega tests have been set-up and namelist file examined to ensure it has the appropriate settings.