DATACMNS-1322 - Cleanup refactorings.

Add missing since tags. Extract methods to maintain single abstraction level per method. Move visitDefaultValue from ClassGeneratingPropertyAccessorFactory to BytecodeUtil. Extend Javadoc.

src/main/java/org/springframework/data/util/ReflectionUtils.java

@@ -410,6 +410,7 @@ public class ReflectionUtils {
 	 *
 	 * @param type must not be {@literal null}.
 	 * @return boxed primitive default value.
+	 * @since 2.1
 	 */
 	public static Object getPrimitiveDefault(Class<?> type) {