Specify short names of ModelVerticalGrid fields in yaml file

[pchakraborty]

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

• Introduced field_edge/center in the yaml config file, so that a model vertical grid is now specified in the yaml file as follows:

  mapl:
    geometry:
      vertical_grid:
        class: model
        standard_name: air_pressure
        field_edge: PLE
        field_center: PL
        units: hPa
        num_levels: 4

• Updated Scenarios tests where a model vertical grid is specified
• Some cleanup of ComponentSpecParser::parse_geometry_spec - vertical grid is parsed in a separate routine now
• Refactored Test_ModelVerticalGrid.F90
• Updated overloaded write of ModelVerticalGrid to include standard name and field names for edge and center variables

Related Issue

[pchakraborty]

Resolves #3184

[pchakraborty]

These edits were included in #3194. Closing this, since #3194 has already been merged.