GFS physics: port SHiELD's progcld6 to radiation scheme#368

Draft

brianhenn wants to merge 4 commits intomasterfrom

gfsrad-port-progcld6

Commits on Jun 16, 2023

port progcld6 and make option to use it with GFS microphysics
brianhenn
committed

Commits on Jun 19, 2023

code cleanup and use SHiELD's constants
brianhenn
committed

Commits on Jun 21, 2023