Support limited area grids in StructuredColumns linear interpolation

[andreapiacentini]

Citing @wdeconinck
This “ComputeNorth” class is used to detect the y-index (or latitude-index) of the latitude North of a given coordinate.
During the construction of this class, it sets up some small arrays to help. It is created for global grids where it is more complicated to deal with extra latitude-rows that are going North of the North Pole (and South of the South Pole).
For a regional grid this should be much simpler, and easy to implement. Just did not get around to it, and nobody had any use case for it, until today