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ARROW-5602: [Java][Gandiva] Add tests for round/cast

- Added java tests for round, cast
- Fixed wrapper fns in cpp to also take out_precision and
  out_scale as args. Not doing this caused a failure in
  docker with llvm-7.

Author: Pindikura Ravindra <ravindra@dremio.com>

Closes #4568 from pravindra/cast_java and squashes the following commits:

e224418a <Pindikura Ravindra> ARROW-5602:  Add tests for round/cast