Make ExtensionTransform ESMF_Field names public character parameters

[darianboggs]

Types of change(s)

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Trivial change (affects only documentation or cleanup)
• Refactor (no functional changes, no api changes)

Checklist

• Tested this change with a run of GEOSgcm
• Ran the Unit Tests (make tests)

Description

The names of the ESMF_Field objects in the ESMF_State objects in subclasses of ExtensionTransform were previously private. This made it difficult to test the subclasses. This PR adds public character parameters for the names.

[tclune]

I think the name parameters should just be in the base class.

Is there any reason to have them vary for subclasses?

[tclune]

I made a suggestion - should just be a simple global replace if you agree.

[darianboggs]

Numerous tests failed. The problem was that the field names were changed from import[1] and export[1] to coupler_import and coupler_export, respectively. I kept the parameter names, but I changed the parameter values back to import[1] and export[1]. The tests pass. Since having public parameters for testing was the goal of this PR, I pushed the changes up, and it's ready for final approval. A future PR can implement the new parameter values, if it is necessary.