New constraint to check type parameter of constaining class

[lars-reimann]

Is your feature request related to a problem?

We need a way to hide methods of a class based on the substitution for some type parameter. This can be used to hide the predict method of models that are not fitted

Desired solution

Add a new constraint:

class Model<State = TrainingState.Unfitted> {
    fun predict() where {
        State sub TrainingState.Fitted
    }
}

• If the constraints is false, but predict is used, show an error. This can be combined with Optional error messages for constraints #1082.
• If the constraint is false, don't suggest the method in code completion.

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