[Java] Push-down filtering in Java

### Push-down filtering (Java) questions

Hey all,

I'm exploring adding push-down filtering to the Java Datasets API, as it currently only supports push-down projection.
Just had a couple of questions before I start this work:

- Is this planned on any current roadmap? I'd like to avoid duplicating work that's already begun
- Does anyone have any smart ideas as to how to pass the filter predicate into ScanOptions? As far as I can tell, the only complication to make this happen would be figuring out some way to call into the Expression object from Java without creating future maintenance effort.

Thanks!

### Component(s)

C++, Java

Commencez par la prise en charge existante de la projection push-down de la Java Datasets API, puis examinez comment ScanOptions et l’objet Expression sont utilisés dans les composants Java et C++. Le travail est terminé lorsque les prédicats de filtre Java peuvent être transmis via ScanOptions pour le filtrage push-down sans créer une charge de maintenance insoutenable.

Rédigé par le modèle d'indexation à partir du texte de l'issue.