To encourage people to migrate their sorting strategy to use the new @SortableField annotation (and encourage feedback about missing functionality), we should have a "strict mode" which exclusively accepts sorting definitions which do not require index un-inverting.

This mode should be enabled by default, but we'll provide a configuration property to still allow the fallback to the previous sorting model.

Eventually we'll need to remove the un-inverting strategy, so I'll rather have such a feature included some versions before doomsday comes.