Fixes #8913 - Review Jetty XML syntax to allow calling JDK methods

Now <Call>, <Get> and <Set> elements can use the "class" attribute
to specify the exact class to perform method lookup.

Improved support for <Property>, <SystemProperty> and <Env> so that
attribute "name" is now optional (as specified in the DTD), and a
"deprecated" attribute may be present instead.
This is necessary to terminally deprecate properties that have
no replacement.

Signed-off-by: Simone Bordet <simone.bordet@gmail.com>

jetty-xml/src/test/java/org/eclipse/jetty/xml/XmlConfigurationTest.java

@@ -36,6 +36,8 @@
 import java.util.stream.Stream;
 import javax.net.ssl.SSLSocketFactory;
 
+import javax.net.ssl.SSLSocketFactory;
+
 import org.eclipse.jetty.logging.JettyLevel;
 import org.eclipse.jetty.logging.JettyLogger;
 import org.eclipse.jetty.logging.StdErrAppender;