* GH-3096: Skip RESOLVABLE_TYPE header in mapping Fixes https://github.com/spring-projects/spring-integration/issues/3096 When we sent an AMQP message we should not map a `JsonHeaders.RESOLVABLE_TYPE` header which is a `ResolvableType` and isn not compatible after converting to string Also improve `JsonToObjectTransformer` to ignore a `JsonHeaders.RESOLVABLE_TYPE` when it is type of String * * Fix `obtainResolvableTypeFromHeadersIfAny()` logic