Allow build operation listeners to log (#4693) This change moves build operation listening out of the standard listener infrastructure, to remove serialisation guarantees. As logging output now causes build operation notifications, whenever a build operation listener logged something it would fail due to the listener manager blocking overlapping signals.
By moving build operation listening out, overlapping and concurrent signals are now allowed. This places more responsibility on listener implementations (e.g. thread safety), but there are few and they are all internal.
Additionally, listeners will now never receive progress notifications before start notifications and after finish notifications for that operation.