SREditor offers classes that are not available for creation

[Red-Cat-Fat]

During the development process, I noticed that SREditor may suggest creating classes that are not available. For example, configs, if they are present in the hierarchy.

InvalidOperationException: Cannot assign an object deriving from UnityEngine.Object to a managed reference. This is not supported.

I think I'll be able to do it next week. I think we should finalize the check by covering it with tests, since this problem may have surfaced after switching to a new visualizer.