Add in java bindings for DataSource

[revans2]

Description

This PR adds DataSource Java bindings. It also fixes a small bug in CUDF that made it so the bindings would not work for anything but CSV.

Checklist

• I am familiar with the Contributing Guidelines.
• New or existing tests cover these changes.
• The documentation is up to date with these changes.

[jlowe]

Partial review

[revans2]

@jlowe please take another look

[revans2]

@davidwendt @vyasr could you please take a quick look at the C++ fix I had to put in to allow parquet/orc reads with a custom data source.

[vuule]

Nice!
What is the motivating use case?

[revans2]

Nice! What is the motivating use case?

I did most of it to try and see if it could help with some memory management pain points. This is one of the few places where we hold onto host memory while allocating GPU memory. It didn't work out exactly how we wanted, but the plan is to try and avoid an extra copy when stitching parts of ORC and parquet together into a final buffer we send to CUDF. It might get expanded to other things in the future.

[revans2]

@vuule could you review the change I had to make to cpp/src/io/utilities/datasource.cpp? It is a C++ change to CUDF do I need a reviewer for it.

[davidwendt]

Approving libcudf C++ change.

[revans2]

/merge