OCI: fix reading of 2D geometries that were always turned as 3D; add a ADD_LAYER_GTYPE=YES/NO layer creation option that defaults to YES to enforce a layer geometry type, and is used to retrieve the layer geometry type when listing layers (#3754)

git-svn-id: https://svn.osgeo.org/gdal/trunk/gdal@27855 f0d54148-0727-0410-94bb-9a71ac55c965