Add water variables

[MayeulDestouches]

This PR extends a few variables related to atmospheric water:

• It extends the 3D mass contents to include a rain, snow, graupel and hail versions.
• It extends the water mixing ratios of water vapor, cloud ice, cloud liquid water and rain by adding variants with the _at_top_interfaces vertical stagger. I only updated the mixing ratios wrt dry air and the mixing ratios wrt moist air and condensed water, as I don't need the mixing ratios wrt moist air alone.

It also adds a few water-related variables:

• Mixing ratios of total water.
• water_vapor_mixing_ratio_wrt_moist_air_and_condensed_water_assuming_saturation for saturated specific humidity.
• derivative_of_ln_water_vapor_partial_pressure_assuming_saturation_wrt_air_temperature for the log derivative of saturation vapor pressure wrt temperature.
• The _at_top_interaces variants of the latter two variables.

[MayeulDestouches]

Tagging @danholdaway for information.

[MayeulDestouches]

Is anything missing for this PR to be merged?

[nusbaume]

Sorry for the slow response! It looks like we still need an approval from @ss421 before we can merge.