FSI Event Handler isn't accessible from the `fsi` object

**Is your feature request related to a problem? Please describe.**
There's a new `OnEvaluation` member on the `FsiEvaluationSessionHostConfig` type that's not accessible from the `fsi` helper object in the same way that a lot of the other `fsi` properties are threaded through.

**Describe the solution you'd like**
I'd like a new member on the `InteractiveSettings` type that could take handler functions and do the plumbing to have those triggered when the evaluation event is triggered. My primary goal here is to make it easier to get `FSharpType` information for values so that bugs like #5992 are more easily explored.

**Describe alternatives you've considered**
Use reflection to both add a handler to the event exposed on the `FsiEvaluationSessionHostConfig`.