polygon triangulation (step 4)

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@31048 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e
4.9.238.0

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@31049 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e