Make LoggingEvent#getFormattedMessage public

[chrylis]

In my test, I want to assert that the log message that is written does not contain specific personal information (this may be present in the object argument, for example, but the object's toString() should not include it in the final written log message). However, the only public API available is direct inspection of the unformatted log arguments.

There exists a method getFormattedMessage() that produces exactly the information I am looking for, but it is marked private. It would be very useful for this method to be public.