make AOT hints for ELC optional

`spring-data-elasticsearch` is also being pulled in as a dependency of
`spring-data-opensearch`. the latter excludes the transient ELC
dependency since it doesn't need it.
if `spring-data-opensearch` (or any downstream project) wants to use AOT
then spring will automatically also pick up the AOT hints from
`spring-data-elasticsearch` - but so far these reference the ELC classes
which have been excluded by `spring-data-opensearch`, thus resulting in
a `ClassNotFoundException`.

this commit makes the registration of these hints dependent on the
presence of the ELC on the classpath. this has no impact on
`spring-data-elasticsearch` consumers which already make use of AOT but
unblocks the usage of AOT for `spring-data-opensearch` and its
consumers.

see also opensearch-project/spring-data-opensearch#441

Author: rursprung

src/main/java/org/springframework/data/elasticsearch/client/elc/aot/ElasticsearchClientRuntimeHints.java

@@ -15,15 +15,9 @@
  */
 package org.springframework.data.elasticsearch.client.elc.aot;
 
-import co.elastic.clients.elasticsearch._types.mapping.RuntimeFieldType;
-import co.elastic.clients.elasticsearch._types.mapping.TypeMapping;
-import co.elastic.clients.elasticsearch.indices.IndexSettings;
-import co.elastic.clients.elasticsearch.indices.PutMappingRequest;
-
 import org.jspecify.annotations.Nullable;
 import org.springframework.aot.hint.RuntimeHints;
 import org.springframework.aot.hint.RuntimeHintsRegistrar;
-import org.springframework.aot.hint.TypeReference;
 import org.springframework.util.ClassUtils;
 
 /**
@@ -38,10 +32,14 @@ public class ElasticsearchClientRuntimeHints implements RuntimeHintsRegistrar {
 	public void registerHints(RuntimeHints hints, @Nullable ClassLoader classLoader) {
 
 		hints.reflection()
-				.registerType(TypeReference.of(IndexSettings.class), builder -> builder.withField("_DESERIALIZER"))
-				.registerType(TypeReference.of(PutMappingRequest.class), builder -> builder.withField("_DESERIALIZER"))
-				.registerType(TypeReference.of(RuntimeFieldType.class), builder -> builder.withField("_DESERIALIZER"))
-				.registerType(TypeReference.of(TypeMapping.class), builder -> builder.withField("_DESERIALIZER"));
+				.registerTypeIfPresent(classLoader, "co.elastic.clients.elasticsearch.indices.IndexSettings",
+						builder -> builder.withField("_DESERIALIZER"))
+				.registerTypeIfPresent(classLoader, "co.elastic.clients.elasticsearch.indices.PutMappingRequest",
+						builder -> builder.withField("_DESERIALIZER"))
+				.registerTypeIfPresent(classLoader, "co.elastic.clients.elasticsearch._types.mapping.RuntimeFieldType",
+						builder -> builder.withField("_DESERIALIZER"))
+				.registerTypeIfPresent(classLoader, "co.elastic.clients.elasticsearch._types.mapping.TypeMapping",
+						builder -> builder.withField("_DESERIALIZER"));
 
 		if (ClassUtils.isPresent("org.apache.http.impl.auth.BasicScheme",
 				ElasticsearchClientRuntimeHints.class.getClassLoader())) {