XmlConfigurationEntryHandler - sonar findings

see https://sonarcloud.io/code?id=apache_sling-org-apache-sling-feature-cpconverter&selected=apache_sling-org-apache-sling-feature-cpconverter%3Asrc%2Fmain%2Fjava%2Forg%2Fapache%2Fsling%2Ffeature%2Fcpconverter%2Fhandlers%2FXmlConfigurationEntryHandler.java

in addition:
the name of the inner class JcrConfigurationHandler extends AbstractJcrNodeParser is confusing. for the sake of consistency it should be named 'JcrConfigurationParser' instead of handler.