DATAREST-1068 - Resize array during merge.

When merging new data into a PersistentEntity, JsonNodes of array types were deserialized into immutable Lists, but the list is later mutated if the source and target arrays are of different sizes. This commit ensures that an array is deserialized into a mutable list.

Original pull request: #371.

spring-data-rest-webmvc/src/main/java/org/springframework/data/rest/webmvc/json/DomainObjectReader.java

@@ -62,6 +62,7 @@ import com.fasterxml.jackson.databind.node.ObjectNode;
  * @author Mark Paluch
  * @author Craig Andrews
  * @author Mathias Düsterhöft
+ * @author Thomas Mrozinski
  * @since 2.2
  */
 @RequiredArgsConstructor
@@ -510,7 +511,7 @@ public class DomainObjectReader {
 		}
 
 		if (source.getClass().isArray()) {
-			return Arrays.asList((Object[]) source);
+			return new ArrayList<>(Arrays.asList((Object[]) source));
 		}
 
 		return null;