LevelSetRayIntersector returns the farthest intersection

The methods of `LevelSetRayIntersector` class (the `intersectIS` and `intersectWS` family) return the first or *closest* intersection of the ray with the levelSet, it would be useful to get the last or *farthest* intersection.

Start by locating the LevelSetRayIntersector class and its intersectIS and intersectWS method families. Trace how they select the first or closest level-set intersection, then define and test equivalent behavior that returns the last or farthest intersection; no specific files or tests are named in the issue.

Written by the indexing model from the issue text.