Extract classes out of SphericalPolygonsSet source file.

None of these classes required private access to the
SphericalPolygonsSet class, so they can be outside, simplifying the
source.

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/math/trunk@1561506 13f79535-47bb-0310-9956-ffa450edef68