Update Kotlin Serialization configuration in HttpMessageConverters

As of As of spring-projects/spring-framework#35733, Spring Framework has
a dedicated method for configuring a Kotlin Serialization converter
specifically.

This commit uses this method instead of configuring the Kotlin
Serialization JSON support as a custom converter. This also removes the
`@Order` on the Kotlin converter bean itself, as there is no need to
order it in the list of custom converters anymore.

Closes gh-47917

module/spring-boot-http-converter/src/main/java/org/springframework/boot/http/converter/autoconfigure/DefaultClientHttpMessageConvertersCustomizer.java

@@ -52,7 +52,7 @@ class DefaultClientHttpMessageConvertersCustomizer implements ClientHttpMessageC
 					builder.withStringConverter(converter);
 				}
 				else if (converter instanceof KotlinSerializationJsonHttpMessageConverter) {
-					builder.addCustomConverter(converter);
+					builder.withKotlinSerializationJsonConverter(converter);
 				}
 				else if (converter.getSupportedMediaTypes().contains(MediaType.APPLICATION_JSON)) {
 					builder.withJsonConverter(converter);

module/spring-boot-http-converter/src/main/java/org/springframework/boot/http/converter/autoconfigure/KotlinSerializationHttpMessageConvertersConfiguration.java

@@ -24,7 +24,6 @@ import org.springframework.boot.autoconfigure.condition.ConditionalOnClass;
 import org.springframework.boot.autoconfigure.condition.ConditionalOnMissingBean;
 import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
-import org.springframework.core.annotation.Order;
 import org.springframework.http.converter.json.KotlinSerializationJsonHttpMessageConverter;
 
 /**
@@ -40,7 +39,6 @@ class KotlinSerializationHttpMessageConvertersConfiguration {
 
 	@Bean
 	@ConditionalOnMissingBean
-	@Order(-10) // configured ahead of JSON mappers
 	KotlinSerializationJsonHttpMessageConverter kotlinSerializationJsonHttpMessageConverter(Json json) {
 		return new KotlinSerializationJsonHttpMessageConverter(json);
 	}