SOLR-839 added XML QueryParser support (deftype=xmlparser) and this ticket here proposes to make that support extensible-via-configuration.
- To support use of custom query builders.
- To support use of custom query builders without a corresponding custom XmlQParser plugin class.
- solrconfig.xml snippet to configure use of the custom builders
- HelloQueryBuilder and GoodbyeQueryBuilder both extend the new abstract SolrQueryBuilder class.