A very few mods (like Entoarox Framework) need temporary access to SMAPI internals pending SMAPI 2.0, but otherwise the internals shouldn't be easily available to mods. If a mod tries to access a SMAPI type through IReflectionHelper, raise an error.

(A mod can use the native C# reflection API to access the internals, but then it's up to them to handle any consequences like breaking internal changes.)

Done in develop for the SMAPI 2.0 release.