Add SurfaceCombiner module

[juliasloan25]

Most of the Regridder module (src/Regridder.jl) will get moved to ClimaUtilities.jl as part of #367. This module has a couple functions which are coupler-specific and should remain in the coupler. We will move these to a new module, SurfaceCombiner, and keep them in the coupler

tracked by https://github.com/CliMA/ClimaUtilities.jl/issues/39

Functions:

• update_surface_fractions https://github.com/CliMA/ClimaCoupler.jl/blob/main/src/Regridder.jl#L406
• combine_surfaces https://github.com/CliMA/ClimaCoupler.jl/blob/main/src/Regridder.jl#L455
• combine_surfaces_from_sol! https://github.com/CliMA/ClimaCoupler.jl/blob/main/src/Regridder.jl#L478