[FR] Add `hidden`/`logLevel` property to Run API events.

[paullewis]

I'm converting from InspectableRunEvent to Run*Event in the .app view, and most of the information is available in both save for the hidden field, which we use to elide inessential information in the Activity Log.

If we could include hidden or maybe the logLevel then I could use that to filter out things like nodeend events from within a Specialist, say. I'm currently using the path, but I'm not sure this is the right approach.