SolrParams ought to have a toLocalParamsString method. I needed such a thing while working on
SOLR-10526 but I thought it deserved it's own issue. In addition, this method needs to call QueryParsing.encodeLocalParamVal but that's in Solr core (not SolrJ) so I think it can be refactored/moved to ClientUtils. I've wanted to call such a method before in client code and there was none. Surprisingly it's only used by FacetComponent within Solr.