GML: add datasource option SRSDIMENSION_LOC=GEOMETRY to be able to write srsDimension attribute on top level geometry element, default on posList unchanged (#5066)

git-svn-id: https://svn.osgeo.org/gdal/trunk@27581 f0d54148-0727-0410-94bb-9a71ac55c965
Merge branch 'trunk' into trunk_travis_macosx