Reverted getSession(id) to public

This method is used by third party session handlers.
Reverts change made as part of #3913

Signed-off-by: Greg Wilkins <gregw@webtide.com>

jetty-server/src/main/java/org/eclipse/jetty/server/session/SessionHandler.java

@@ -886,7 +886,7 @@ public class SessionHandler extends ScopedHandler
      * @param id The session ID stripped of any worker name.
      * @return A Session or null if none exists.
      */
-    protected Session getSession(String id)
+    public Session getSession(String id)
     {
         try
         {