Expose tracing visitor via plugin so it can be used with unbranded emitter

[JoshLove-msft]

AI libraries are going to be using the unbranded emitter but they should still have tracing support. The one thing we will have to handle differently is how we check if tracing is enabled.

[JoshLove-msft]

This doesn't need to be done as we can wait until the unbranded generator supports tracing.