Make JpaSort.unsafe operational.

We have offered this method as a way for people to customize an ORDER BY clause beyond a simple property name. For example, someone could use "LENGTH(firstname)" as a function to order by the length of each row's lastname instead of ordering by the lastname itself.

By using the relevant parser and applying a different visitor, this commit make operational a feature that shows little evidence of ever having worked.

See #3172.

Author: gregturn