[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

从 Java Datasets API 现有的下推投影支持开始，然后检查 ScanOptions 和 Expression 对象在 Java 与 C++ 组件中的使用方式。当 Java 过滤谓词可以通过 ScanOptions 传递，以实现下推过滤，同时不会造成难以持续的维护负担时，工作即告完成。

由索引模型根据 Issue 内容生成。