Add regression test for CaptionActor2D.

Also update the Rendering/Annotation/Testing/Cxx/CMakeLists.txt file
to allow the new interactor override to work with the tests for this
module.

Change-Id: I77bdf2cd4baac80ae06faad09867d289e4c70505
Merge topic 'CaptionActorTest' into master

30cc7461 Add regression test for CaptionActor2D.