Handle over-180-degrees cells without treating edges as latlon-aligned

[pp-mo]

Seeing comment here

In addition, ESMF cannot handle any cells covering >=180 degrees, e.g. longitudes -180..+180 : such cases will give errors : These cases can be fixed by specifying resolution=2.

While that statement is all very well, it is in that case simply not doing the same calculation.

So, suppose I have a cell with an edge that runs (-120, -30) to (+120, +30) : I might actually want that line to be on a great circle, and more especially if the boundaries are not generally along lines of latitude or longitude. I can in principle achieve that by taking a different intermediate point, which lies on the GC instead of the 'straight latlon' line. But obviously, this is not what the resolution keyword provides.

In fact, this could occur any time a target may have cells which are "large" but not specially latlon-aligned, and it particular when their edges are supposed to be on GCs rather than some 'straight latlon' line.

In effect, this is due to the conflation of the "two problems" I mentioned in the above comment : that of handing overlarge cells, and of approximating 'straight latlon' boundary lines.

So "ideally", we could provide an additional keyword that controls whether the boundaries of over-large cells are divided along a latlon line, or on a GC.
E.G. a new key likeresolve_latlon=True, for both GridToMeshESMFRegridder and MeshToGridESMFRegridder

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