Implement fieldmap option in ogr2ogr (#5021)

git-svn-id: https://svn.osgeo.org/gdal/trunk@25733 f0d54148-0727-0410-94bb-9a71ac55c965
Add autotest for the fieldmap setting (#5021)

git-svn-id: https://svn.osgeo.org/gdal/trunk@25734 f0d54148-0727-0410-94bb-9a71ac55c965