[Enhancement]: Allow users to pass regridding weights

[jasonb5]

Is your feature request related to a problem?

n/a

Describe the solution you'd like

This would add a weights parameter to the horizontal regridder that would accept pre-calculated weights. The xESMF library already supports this and this would be trivial to add to Regrid2. This is not currently an option for the xgcm regridder.

Describe alternatives you've considered

No response

Additional context

No response

[jasonb5]

@pochedls @lee1043 @tomvothecoder The xESMF regridder will accept a sparse array, dict, str, Path, or Dataset. Any preference to which of this we'd like to support?

[pochedls]

I think my preference would be either a Dataset or a str argument (to a netcdf dataset).

[lee1043]

Dataset, data array, and path to netcdf file would be my picks.

[tomvothecoder]

Dataset, data array, and path to netcdf file would be my picks.

This one sounds good to me.

[jasonb5]

This sounds reasonable to me.