Changes to make JPAAbstractExpandQuery available for extension

[VMatyushevski]

Feature added: To support the addition of custom SQL Hint to the search query. Approach considered: Upon trying out different options, we have chosen to extend JPAAbstractExpandQuery and add our custom hint during execute() method call. Overview of the changes: The current design (especially modifiers) of JPAAbstractExpandQuery doesn`t fully support extension since the Class by itself is public, but the important methods that are used within an extention and other dependent classes have package private access. So the changes are specific to the classes or methods that are involved in supporting the mentioned feature. @wog48, Please review the PR. If you have another approach to enabling the above feature, we are open to considering it.

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