Add heat content associated with Forr_rofl_glc and Forr_rofi_glc

[gustavo-marques]

Following the implementation of glc->ocn coupling via going through mosart (#463), the heat content (or enthalpy) associated with these fields must be computed and provided to OCN. here is a PR that can be used as an example of adding enthalpy fields in CMEPS.

For now, we can compute Foxx_rofl_glc following what's done for Foxx_hrofl. Similarly for Foxx_rofi_glc and Foxx_hrofi.

These changes are needed for NCAR/MOM6#288