clone Schema using AnnotationUtils.clone with WA

Getter and setter of Schema's example field works with Object class, this breaks serializer added in https://github.com/OpenAPITools/openapi-generator/pull/18052. I've replaced it with AnnotationUtils.clone call with some workaround for custom types for schema ver < 3.1 (looks like this method works fine with 3.1 schemas https://github.com/OpenAPITools/openapi-generator/pull/18052#discussion_r1600905187)

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```
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```
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OpenAPITools / openapi-generator