Use List.of() for JavaTypeMapper.TRUSTED_PACKAGES

* Improved the immutable field `TRUSTED_PACKAGES` in the `DefaultJackson2JavaTypeMapper` class to a `List.of()` method that returns an `ImmutableList`.
* Remove unused import `DefaultJackson2JavaTypeMapper`

Author: ch4570

spring-kafka/src/main/java/org/springframework/kafka/support/mapping/DefaultJackson2JavaTypeMapper.java

@@ -16,7 +16,6 @@
 
 package org.springframework.kafka.support.mapping;
 
-import java.util.Arrays;
 import java.util.LinkedHashSet;
 import java.util.List;
 import java.util.Set;
@@ -45,11 +44,7 @@
 public class DefaultJackson2JavaTypeMapper extends AbstractJavaTypeMapper
 		implements Jackson2JavaTypeMapper {
 
-	private static final List<String> TRUSTED_PACKAGES =
-			Arrays.asList(
-					"java.util",
-					"java.lang"
-			);
+	private static final List<String> TRUSTED_PACKAGES = List.of("java.util", "java.lang");
 
 	private final Set<String> trustedPackages = new LinkedHashSet<>(TRUSTED_PACKAGES);
 
@@ -78,7 +73,7 @@ public void setTypePrecedence(TypePrecedence typePrecedence) {
 	 */
 	@Override
 	public void addTrustedPackages(String... packagesToTrust) {
-		if (this.trustedPackages.size() == 0) {
+		if (this.trustedPackages.isEmpty()) {
 			return;
 		}
 		if (packagesToTrust != null) {