DATACMNS-1779 - Consider kotlin.Unit a simple type.

kotlin.Unit is now considered a simple type to avoid PersistentEntity creation.

ReflectionUtils.isVoid(…) now encapsulates the check so that calling code doesn't need to check if Kotlin is on the class path.

src/main/java/org/springframework/data/mapping/model/SimpleTypeHolder.java

@@ -156,7 +156,7 @@ public class SimpleTypeHolder {
 
 		String typeName = type.getName();
 
-		if (typeName.startsWith("java.lang") || type.getName().startsWith("java.time")) {
+		if (typeName.startsWith("java.lang") || type.getName().startsWith("java.time") || typeName.equals("kotlin.Unit")) {
 			return true;
 		}