addition of flux area correction factors

[mvertens]

This PR adds area flux correction factors as is done in CPL7. Remove some debug writes of coupler fields. And remove state_getfldptr as it was unused.

Also sets the number of OpenMP threads according to the coupler namelist rather than env variables.

[billsacks]

Thanks @ekluzek . Note that the changes to threading are only in the nuopc cap, and threading with nuopc currently is not covered in our aux testing.

[billsacks]

I discussed this with @mvertens . She pointed out that you don't always want to do the area correction – such as for states. We came up with an interface to these routines that I like better to handle this:

• Don't pass the area correction factors; instead, use the module variables (this way you don't accidentally mix up which area correction factor to use for the import/export)
• Add a new, required argument: do_area_correction; the area correction will be applied if this is true. By making it required, we force someone adding a new field to consider whether it should be true or false for their new field.

[billsacks]

I have confirmed that my refactor did not change answers for the test SMS_D_Ld5_Vnuopc.f10_f10_mg37.I2000Clm50BgcCrop.cheyenne_intel.mosart-default, which I ran in the context of CESM's nuopc_dev branch. I will merge this shortly.