Add immersion freezing

[tangwhiap]

Add the immersion freezing simulation codes, freezing test case, and freezing scenario.

[slayoo]

@tangwhiap, codecov reports here that the following three cases are never tested:

• if (env_state%temp > const%water_freeze_temp) never occurs in ice_nucleation_melting
• if (aero_particle_new%frozen) never occurs in aero_particle_coagulate
• if (immersion_freezing_scheme_type == IMMERSION_FREEZING_SCHEME_ABIFM) in ice_nucleation_immersion_freezing_time_dependent_naive

Also, there are two instances where the following comment is placed:

! FIXME: Do this to avoid compiler warning/error, fix it in the future.

[slayoo]

melting covered!

[jcurtis2]

• if (immersion_freezing_scheme_type == IMMERSION_FREEZING_SCHEME_ABIFM) in ice_nucleation_immersion_freezing_time_dependent_naive

This appears to be a false-positive in codecov as I've added print statements that are printed when running test_freezing_4.sh. I tried a few things to try to reorganize the code so it might detect that it is indeed tested with line continuations and optimization reduction.

Also, there are two instances where the following comment is placed:

! FIXME: Do this to avoid compiler warning/error, fix it in the future.

I've changed this to a WORKAROUND so that we do not actually insinuate that we can fix this problem 48b0a85 rather than a FIXME.