Make sure @ClientExceptionMapper works properly in native mode

Fixes: #23766

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

@@ -224,6 +224,7 @@ void registerProvidersFromAnnotations(CombinedIndexBuildItem indexBuildItem,
             BuildProducer<GeneratedBeanBuildItem> generatedBeans,
             BuildProducer<GeneratedClassBuildItem> generatedClasses,
             BuildProducer<UnremovableBeanBuildItem> unremovableBeans,
+            BuildProducer<ReflectiveClassBuildItem> reflectiveClasses,
             RestClientReactiveConfig clientConfig) {
         String annotationRegisteredProvidersImpl = AnnotationRegisteredProviders.class.getName() + "Implementation";
         IndexView index = indexBuildItem.getIndex();
@@ -292,6 +293,7 @@ void registerProvidersFromAnnotations(CombinedIndexBuildItem indexBuildItem,
                             + "' is allowed per REST Client interface. Offending class is '" + result.interfaceName + "'");
                 }
                 ifaceToGeneratedMapper.put(result.interfaceName, result);
+                reflectiveClasses.produce(new ReflectiveClassBuildItem(true, false, false, false, result.generatedClassName));
             }
 
             for (Map.Entry<String, List<AnnotationInstance>> annotationsForClass : annotationsByClassName.entrySet()) {

integration-tests/rest-client-reactive/src/main/java/io/quarkus/it/rest/client/main/HelloClient.java

@@ -1,16 +1,29 @@
 package io.quarkus.it.rest.client.main;
 
 import javax.ws.rs.Consumes;
+import javax.ws.rs.NotFoundException;
 import javax.ws.rs.POST;
 import javax.ws.rs.Path;
 import javax.ws.rs.Produces;
 import javax.ws.rs.QueryParam;
 import javax.ws.rs.core.MediaType;
+import javax.ws.rs.core.Response;
+
+import io.quarkus.rest.client.reactive.ClientExceptionMapper;
 
 @Path("")
 public interface HelloClient {
     @POST
     @Produces(MediaType.TEXT_PLAIN)
     @Consumes(MediaType.TEXT_PLAIN)
     String greeting(String name, @QueryParam("count") int count);
+
+    // this isn't used, but it makes sure that the generated provider can be properly instantiated in native mode
+    @ClientExceptionMapper
+    static RuntimeException toException(Response response) {
+        if (response.getStatus() == Response.Status.NOT_FOUND.getStatusCode()) {
+            return new NotFoundException("not found");
+        }
+        return null;
+    }
 }