Fix native issue with @providers when only the REST Client exists

When the server part of Quarkus REST is not included, prior to
this change, user's @Provider classes were not registered
for reflection

Relates to: quarkiverse/quarkus-langchain4j#722

extensions/resteasy-reactive/rest-client/deployment/src/main/java/io/quarkus/rest/client/reactive/deployment/RestClientReactiveProcessor.java

@@ -311,6 +311,10 @@ void registerProvidersFromAnnotations(CombinedIndexBuildItem indexBuildItem,
                                     int.class),
                             constructor.getThis(), constructor.loadClassFromTCCL(providerDotName.toString()),
                             constructor.load(priority));
+
+                    // when the server is not included, providers are not automatically registered for reflection,
+                    // so we need to always do it for the client to be on the safe side
+                    reflectiveClassesProducer.produce(ReflectiveClassBuildItem.builder(providerDotName.toString()).build());
                 }
             }