OpenFileGDB: fix GetFeatureCount() to take into account real geometry when a spatial filter is set (not only its MBR). And build the spatial index while we are at it for potential later GetNextFeature() calls. Fix wrong polygon test data and add a more interesting layer with non identical polygons. Better test spatial filter support too

git-svn-id: https://svn.osgeo.org/gdal/trunk/gdal@26843 f0d54148-0727-0410-94bb-9a71ac55c965