Having MDC in LoggingEvent for unit tests

[tdeverdiere]

It would be handy to have the Map Diagnostic Context (MDC) in org.slf4j.event.LoggingEvent so it's easier to test the logs in unit tests.
I use logunit which has no dependency on logback, nor log4j2. But it uses slf4j to return the results of the logs to test. So the test assertions are done on LoggingEvent.
I raise an issue in logunit : netmikey/logunit#5 , but it would be easier if LoggingEvent could have this method. This would avoid to implement a specific LogEvent class in logunit.