Add accommodation coefficient and molecular diffusion constant fields to GasSpecies?

[jeff-cohere]

We are starting to collect some parameters that characterize the behavior of gas particles. At some point, we should discuss whether to add these parameters to the definition of a gas species.

[overfelt]

From gas/aerosol exchange
// ratio of gas uptake coeff w.r.t. that of h2so4
static constexpr Real h2so4_h2so4_uptake_coeff_ratio = 1.00; // for SOAG
static constexpr Real soag_h2so4_uptake_coeff_ratio = 0.81; // for SOAG
static constexpr Real nh3_h2so4_uptake_coeff_ratio = 2.08; // for NH3

[pbosler]

Gas accommodation coefficients for mass transfer (via molecular mean path diffusion) and thermodynamics transfer also appear in the droplet activation process. In mam4 ndrop.F90, their values are magic constants in the .F90 files; you wouldn't know what they are unless you read the derivation papers that describe the parameterization. However, for droplet activation the gases are dry air and water vapor and the literature disagrees on their correct values.