Make a Swath definition subclass for interpolated data

Feature description

A lot of data we use in our team has geolocation data provided as with tiepoints to interpolate. Python-geotiepoints works as expected for this and it's easy to create a swath definition base on dask arrays (so that the navigation data can be interpolated chunk-wise).

However, for some applications it would be preferable to be able to have access to the interpolation function directly in the swath definition. For example, for computing a granule ring or for getting just a few points out of the data, it would be desirable to interpolate on a case by case basis.

For this, I propose creating a subclass of the Swath definition that would take on initialisation the lower-resolution lon and lat arrays along with a function to call to get interpolated values for a given position in the array.
From there, re should be able have a custom get_lonlat method that does the interpolation itself if the number of requested points is smaller than say 100 points.