JERSEY-847: Entity of the response will always be empty when resource methods return type is java.io.Reader.

 - Fix + Reproducer Test (both migrated from 2.x).

Change-Id: Ie255a22d9a6ece7969a1730cf5f8e0419523e8b7
Merge "JERSEY-847: Entity of the response will always be empty when resource methods return type is java.io.Reader."