[FEA][JNI] Add JNI bindings for cudf::split

In order to test scenarios where non-contiguous split would be more appropriate than `cudf::contiguous_split` (e.g. potentially for large tables where a contiguous split would force large allocations per split), I would like to add JNI bindings to `cudf::split`.

I have this coded up, but I do need to add a test. I should have a PR today or tomorrow at the latest.

Proposing `splitAndCopy` at the `Table` level, which means we would copy the table views returned by `cudf::split` to make them owning tables.