TupleTransformer

The constructor syntax in JPQL is limited by the fact, that the class must be visible to the classloader of the persistence provider. Also one might want to apply a custom transformation strategy based on metadata that does not use constructors but factories, builders or setters. To overcome these limitations I propose the addition of a TupleTransformer interface which can be implemented by a user to provide custom strategies.

```
**TupleTransformer.java**public interface TupleTransformer {
List transform(List tuples);
X transform(Tuple tuple);
}
```

and an addition to Query and TypedQuery:

```
**Query.java**public interface Query {
// other methods
Query setTupleTransformer(TupleTransformer tupleTransformer);
}
```
```
**TypedQuery.java**public interface TypedQuery extends Query {
// other methods
TypedQuery setTupleTransformer(TupleTransformer tupleTransformer);
}
```

For reference see the ResultTransformer of Hibernate: [http://docs.jboss.org/hibernate/orm/4.3/javadocs/org/hibernate/transform/ResultTransformer.html](http://docs.jboss.org/hibernate/orm/4.3/javadocs/org/hibernate/transform/ResultTransformer.html)

Start with the proposed TupleTransformer interface and the setTupleTransformer signatures in Query and TypedQuery. Compare the requested API with Hibernate's referenced ResultTransformer, then clarify the transformation behavior and integration points; done means the persistence API supports the agreed custom tuple-transformation strategy.

Written by the indexing model from the issue text.