Add real_copy_set to diag_util_mod

[ganganoaa]

Description
Adds a generic public routine, real_copy_set(), to the diag_util_mod and deletes it from the fms_diag_object_mod.

Fixes # (issue)
CI

How Has This Been Tested?
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Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• Any dependent changes have been merged and published in downstream modules
• New check tests, if applicable, are included
• make distcheck passes