`PrivateMethodOrAccessorAdd` call in `ClassDefinitionEvaluation` can throw

[mhofman]

Hi you also need to change ! to ? in https://tc39.es/ecma262/#_ref_8028 (ClassDefinitionEvaluation)

Originally posted by @Jack-Works in #6

More precisely, static element evaluations in step 26 (like a static block) can make F non-extensible, which would result in PrivateMethodOrAccessorAdd in step 31 now throwing.

[mhofman]

Actually I think I misread ClassDefinitionEvaluation and the evaluation of class elements does not execute user code at that state. I'm actually unsure how it could result in an abnormal completion. Anyway, I don't think there is a way for the class to become non-extensible before the private static method / accessors are added, and since the class itself is an ordinary function, IsExtensible itself also wouldn't throw. It might be worth adding an editor note to clarify this.