Add & fix SQL tracing

- #3147
If we want the base class to trace from its source, we shouldn't have a virtual `Trace` property to begin with.

The only two classes that that were using the `Trace` property were `MessageBus` and `SqlMessageBus`. `SqlMessageBus` no longer uses the property, and `MessageBus` can just use the private field since the virtual property it is currently using is never overridden as far as I can tell.