Fix Kotlin Serialization converter registration logic

This commit fixes Kotlin Serialization converter
registration logic in RestTemplate,
AbstractMessageBrokerConfiguration and
AllEncompassingFormHttpMessageConverter classes
to be similar to the one in
WebMvcConfigurationSupport.

Closes gh-29008

spring-web/src/test/java/org/springframework/web/client/RestTemplateTests.java

@@ -51,6 +51,8 @@ import org.springframework.http.client.ClientHttpResponse;
 import org.springframework.http.client.SimpleClientHttpRequestFactory;
 import org.springframework.http.converter.GenericHttpMessageConverter;
 import org.springframework.http.converter.HttpMessageConverter;
+import org.springframework.http.converter.json.KotlinSerializationJsonHttpMessageConverter;
+import org.springframework.http.converter.json.MappingJackson2HttpMessageConverter;
 import org.springframework.util.StreamUtils;
 import org.springframework.web.util.DefaultUriBuilderFactory;
 
@@ -103,6 +105,16 @@ class RestTemplateTests {
 		template.setErrorHandler(errorHandler);
 	}
 
+	@Test // gh-29008
+	void defaultMessageConvertersWithKotlinSerialization() {
+		RestTemplate restTemplate = new RestTemplate();
+		List<HttpMessageConverter<?>> httpMessageConverters = restTemplate.getMessageConverters();
+		assertThat(httpMessageConverters).extracting("class").containsOnlyOnce(
+			KotlinSerializationJsonHttpMessageConverter.class,
+			MappingJackson2HttpMessageConverter.class
+		);
+	}
+
 	@Test
 	void constructorPreconditions() {
 		assertThatIllegalArgumentException()