Rename org.apache.logging.log4j.core.LogEvent.getFQCN() to getLoggerFQCN() to match using “Logger” in getLoggerName(), otherwise get the FQCN of what? Not the event, the logger _of_ the event, hence this change.

git-svn-id: https://svn.apache.org/repos/asf/logging/log4j/log4j2/trunk@1593567 13f79535-47bb-0310-9956-ffa450edef68