Complete functionality for flag_xyfill in CAM-SIMA

[peverwhee]

The flag_xyfill functionality in CAM enables history output with the fillvalue applied to points that are non-applicable for the field. The infrastructure for this exists in CAM-SIMA, but it is not fully hooked up. Until completed, the results of some history fields will not match what's in CAM.

For example, in RRTMGP, the cloud diagnostics (TOT_CLD_VISTAU, etc).