[VL] Separate each jni wrapper to different files

[Yohahaha]

Description

JniWrapper.cc is too large and may be larger in the future, we could separate it into sub dirs when some stateful static variables be removed, and get benefits from readability and UT.

[Yohahaha]

After issue 3077 completed, I will separate current JniWrapper.cc into different sub-dir, it will looks like below:

cpp
  |- jni
  |- memory
  |- compute
    |- r2c
      |- R2CJniWrapper.cc
      |- Row2Columnar.h
      |- test
      |- benchmark
    |- c2r
      |- C2RJniWrapper.cc
      |- Columnar2Row.h
      |- ...
    |- shuffle
      |- ShuffleReaderJniWrapper.cc
      |- ShuffleReader.h
      |- ShuffleWriterJniWrapper.cc
      |- ShuffleWriter.h
      |- ...
    |- serializer
    |- wholestage
    |- [common files]
  |- ...

Any suggestions? @jinchengchenghh @zhztheplayer @rui-mo

[zhztheplayer]

This sort of refactor is needed.

The thing is that we should find a proper time to apply the change, since it may easily conflict with other pending PRs.

[Yohahaha]

The thing is that we should find a proper time to apply the change, since it may easily conflict with other pending PRs.

Good point, I prefer do the refactor in weekend, before that, let's discuss the structure we expected.

[Yohahaha]

Also cc @ulysses-you @FelixYBW @zhouyuan

[ulysses-you]

I think make jni file name align with java class is good. The VexloJniWrapper should also be taken into account. e.g., The java class PlanEvaluatorJniWrapper has several jni methods that map to both JniWrapper and VexloJniWrapper. What's the really difference between VexloJniWrapper and JniWrapper ?

[zhztheplayer]

The java class PlanEvaluatorJniWrapper has several jni methods that map to both JniWrapper and VexloJniWrapper.

PlanEvaluatorJniWrapper -> VeloxJniWrapper

Such mappings should be finally eliminated IIUC. We already had Backend and ExecutionCtx as the APIs across backends.