Add support to retrieve JPQL query from Query object

Currently the interfaces javax.persistence.criteria.AbstractQuery and javax.persistence.Query have no support for retrieving the underlying JPQL Query for additional transformation which would be, especially for named queries, very useful! Just think of the fact, that you currently have to copy and paste a named query if you like to have exactly the same query with an additional predicate in the where clause. The predicate in the where clause is just an example, there are probably tons of use cases where this feature would be helpful and minimize redundant code!

I would suggest to add the following methods:

```
**Query.java**public interface Query{
// currently available methods...
public String getQuery();
}
```
```
**AbstractQuery.java**public interface AbstractQuery{
// currently available methods...
public String getQuery();
}
```

Start by reading the javax.persistence.Query and javax.persistence.criteria.AbstractQuery interface definitions and the existing issue discussion. Determine the API and specification implications of exposing the underlying JPQL, including how the proposed getQuery() method would be defined. Done means the proposal has an agreed scope and corresponding specification changes and tests.

Written by the indexing model from the issue text.