SolrJettyServer is a very useful way of running Solr within an application or test. However, it does not really need to be included in Solr Core. It can be provided in the test-framework module, so that Solr Core does not need to depend on Jetty Server jars.
This will allow Solr to put all shared server & Solr (web-app) dependencies in server/lib/ext/.
However, as noted in the Github PR, Jetty does not allow "server" classes (including the classes in jetty-io, jetty-util, jetty-http, etc) to be used by the web-app (Solr) and the jetty server. Therefore we need to explicitly remove this restriction when we implement this.