Previously, Slf4jLoggingSystem would install SLF4JBridgeHandler into
JUL but would only remove a single root handler that was a
ConsoleHandler. If there were was than one root handler or the single
root handler was of a different type, they would not be uninstalled.
When deploying an application to Tomcat, this led to duplicate log
messages appearing in Tomcat’s console output and to logging from
other application or Tomcat itself being routed into an
application-specific log file enabled using the logging.file
configuration property.

A secondary, related problem was that LogbackLoggingSystem installs a
LevelChangePropagator so that Logback’s log level configuration is
propagated into JUL. This meant that an individual Boot app with
custom log level configuration could change the log levels of Tomcat
itself and of any other applications that had been deployed to Tomcat
and use JUL.

This commit updates both Slf4jLoggingSystem and LogbackLoggingSystem
so that they only change JUL’s configuration if it hasn’t already been
customized. The configuration is deemed to have not been customised if
there’s a single root handler and its a console handler.

Closes gh-13470