Expose spatial SerializedDVStrategy as a Solr PostFilter

The new SerializedDVStrategy in lucene-spatial allows storing serialized shape/geometry in DocValues to get very precise matches. It's mostly for storing polygons & line strings in the index. It needs a Solr FieldType and a means to use it as a Solr PostFilter so that it gets executed last. Maybe even add some kind of Shape cache configurable in solrconfig.xml for frequently looked-up shapes too.