Add ALIAS column to ACG StateSpec files

[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

This PR adds the capability to the automatic code generator (ACG) to give an alternate name to the pointer variable in the pointer declaration and MAPL_GetPointer call for a variable spec. The default behavior is to create a pointer variable FOO for a variable spec with short_name=FOO. If the ALIAS column is added to the ACG StateSpec file and the value for a row is not blank, that value is used for the pointer variable if the -d and/or -g options are included in the ACG call.

This PR was created in response to variable specs that include the same NAME (short_name) for variables in two categories (eg. IMPORT and EXPORT). It creates a more general capability to name the pointer variable.