Should we now allow constants in the FORTRAN code be all uppercase? And start making that change in the code?

As discussed here:

https://github.com/ESCOMP/CTSM/pull/2401#discussion_r1514954169

There's a desire to use all uppercase for constants in the FORTRAN code. I do find this nicely readable. But, as discussed above we didn't allow it because ALL uppercase was reserved for CPP tokens. However, we almost don't have any CPP tokens in the code anymore. And haven't for at least a decade now? So maybe we could start allowing it?

And as a future cleanup after CESM3 do we move to making this change for all constants?