P3 heterogeneous freezing code to-do list

[singhbalwinder]

From @mahf708 comment

1. Harmonize naming scheme for tendencies along the lines of @brhillman's comment (so making these variable names consistent in the cpp impl, EAMxx: Adds aerosols heterogeneous freezing calculations in P3 microphysics #6947 (comment))

2. Add technical docs from the description of the pr to the components/eamxx/docs dir (so that they can appear on docs.e3sm.org/E3SM, EAMxx: Adds aerosols heterogeneous freezing calculations in P3 microphysics #6947 (comment))

3. Tracking on mmf2 test; while the fail isn't apparent now, this pr will break mmf2 testing