Provide tools to compare rendition targets

I.e. allow library users to answer the questions:
- “is this annotation targeted by the rendition”?
  (Similarly to qt5/qt6’s LinkRendition::isReferencedAnnotation(...))
- “is this media played by the rendition”?
  Allows to know whether we apply operand (play/pause/stop) on a
  rendition already shown or whether we need to replace it with another
  media.

This requires extending the rendition action with private fields to
store refs to the screen annotation and media rendition.

These fields have been added in an ABI-compatible structure, similary to
existing code for PopplerRectangleExtended.
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