Align HttpMessageConverters builder with WebFlux codecs variants

As of #33894, we introduced a new `HttpMessageConverters` API.
While this achieved our goal of focusing converters classpath detection
in a single place and avoiding waste, a single `HttpMessageConverters`
instance for both client and server added more complexity for developers.

This commit aligns the API here with the WebFlux `CodecsConfigurer` to
opt for a client/server flavor as the first step in the builder.
While this make the sharing of converter instances between server and
client impossible, this allows for a simpler API and separates concerns.

Closes gh-35187

Author: bclozel

framework-docs/src/main/java/org/springframework/docs/web/webmvc/mvcconfig/mvcconfigmessageconverters/WebConfiguration.java

@@ -34,7 +34,7 @@
 public class WebConfiguration implements WebMvcConfigurer {
 
 	@Override
-	public void configureMessageConverters(HttpMessageConverters.Builder builder) {
+	public void configureMessageConverters(HttpMessageConverters.ServerBuilder builder) {
 		JsonMapper jsonMapper = JsonMapper.builder()
 				.findAndAddModules()
 				.enable(SerializationFeature.INDENT_OUTPUT)

framework-docs/src/main/kotlin/org/springframework/docs/web/webmvc/mvcconfig/mvcconfigmessageconverters/WebConfiguration.kt

@@ -16,7 +16,7 @@ import java.text.SimpleDateFormat
 @Configuration
 class WebConfiguration : WebMvcConfigurer {
 
-	override fun configureMessageConverters(builder: HttpMessageConverters.Builder) {
+	override fun configureMessageConverters(builder: HttpMessageConverters.ServerBuilder) {
 		val jsonMapper = JsonMapper.builder()
 			.findAndAddModules()
 			.enable(SerializationFeature.INDENT_OUTPUT)