OneOfs are not resolved in subtypes

[aykborstelmann]

Describe the bug

Given a super type and a subtype, if you use another supertype on a property of the subtype it is not resolved using oneOfs correctly, as the org.springdoc.core.converters.PolymorphicModelConverter should do.

This is because io.swagger.v3.core.jackson.ModelResolver#resolveSubtypes in ModelResolver:1542 does create the AnnotatedType with (implicitly) resolveAsRef=false.

Thus the ref is never set and thus resolvedSchema.get$ref() == null is false in PolymorphicModelConverter.java:79 and no oneOfs are resolved as expected.

[aykborstelmann]

If verified that this is indeed a bug, I am willing to propose a solution, by adding a

    if (type.getParent() != null) {
      type.setResolveAsRef(true);
    }

at the start of PolymorphicModelConverter#resolve.

[aykborstelmann]

I see, this is a duplicate of #2597. Closing this in favor of #2597