Add an internal helper to redirect java.util.logging to SLF4J

Add an internal helper (org.xwiki.logging.internal.JavaUtilLoggingBridge, in xwiki-commons-logging-api) to redirect the logs produced with java.util.logging to SLF4J: it replaces the handlers of the java.util.logging root logger with SLF4J's SLF4JBridgeHandler, and puts them back when uninstalled.

It relies on org.slf4j:jul-to-slf4j, whose version is now managed like the other SLF4J bridges, and which is an optional dependency of xwiki-commons-logging-api (the applications using the helper need to depend on it themselves).

It's used by XWiki Platform to redirect the java.util.logging logs to SLF4J (XWIKI-25494).