Adding constants for SHiELD microphysics

[oelbert]

Description
the SHiELD model uses a different set of heat capacities (calculated at 0 C instead of 15 C) for calculations, and also introduces a new physics constants to use in calculations. This PR adds the new constants and a SHiELD constants version to select the correct heat capacities and derived constants.

How Has This Been Tested?
The SHiELD microphysics tests were run using this branch

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

Was still in draft