Allow driver to accept multiple forms of precipitation data

[SnowHydrology]

Currently, the 1D Noah-OWP-Modular driver reads in precipitation rate, which it assigns to PRCP in the AsciiReadModule and then to PRCPNONC in AtmProcessing. For Nextgen compatibility, there is a compiler directive in AtmProcessing that toggles between PRCP and PRCPNONC depending on the NGEN_FORCING_ACTIVE flag.

We should allow the driver to accept constituent types of precipitation for when/if it's forced by a weather model that provides multiple forms of precipitation.

We should also evaluate whether computing the fraction of a grid cell receiving precipitation (water%fp) is appropriate for smaller scale modeling.