Evaluate the land model only where land exists

[juliasloan25]

In offline (land-only) runs, ClimaLand passes a land/sea mask to its ClimaCore space, so that the land model is only evaluated where land is actually present. By contrast, in coupled runs we currently evaluate the land model over the entire surface of the planet. This is an easy way we can improve the performance of the land model by 3x.

Work involved

• Receive a land/sea mask from the ocean model (see Pass land/sea mask to component models #1838)
• Update make_land_domain to take in a land/sea mask (this might need to be a NetCDF file, unless we change how ClimaLand/ClimaCore accepts the mask), and pass it to CL.Domains.global_domain. To avoid gaps along continent boundaries, the threshold for the mask should be 0 - i.e. anywhere that any amount of land is present, evaluate both the land model and the ocean model)