Add r2SCAN-3c and wB97X-3c parameters about dftd4

[marvinfriede]

I added a check for r2SCAN-3c before get_rational_damping collects the damping parameters (including s9, so we set it before). This way, we do not break the API of new_d4_model, which is not necessary for a single functional in my opinion. The additional code also checks if --zeta or --mbdscale are set via command line, so they can still be overwritten for r2SCAN-3c, i.e., command line arguments have priority.

[marvinfriede]

I added the D4 parameters for both functionals (#220).

However, for r2SCAN-3c, two parameters of the charge-scaling function ("ga": 2.00, "gc": 1.00) as well as the MBD-scaling ("s9": 2.0) must be modified. These cannot be set internally, but must be specified via the command line interface (--mbdscale 2.0 --zeta 2.0 1.0). Should we just leave that to the user?

[TyBalduf]

I think it would be confusing for the end user if specifying -f r2scan didn't result in the correct D4 parameters/model.

It seems like s9 could be modified internally around here: https://github.com/dftd4/dftd4/blob/main/src/dftd4/param.f90#L210
Essentially, just checking for the functional id for any special cases where s9 should be modified and setting it before get_d4eeq_*_parameters is called.

Updating ga and gc is a little trickier. If changing the D4 model parameters is something that will be done more often for later functionals, it would maybe make sense to have new_d4_model accept a method argument as well. But if we assume this is a one off case, then just checking for the method before the call to new_d4_model in the app and replacing ga and gc would be enough.