[FEA] Implement chunked_pack

[abellina]

In spark-rapids, we use cudf::pack (in reality we cudf::contiguous_split with empty splits) to layout a cudf table with its various data, validity, offsets buffers and potential children, into a contiguous buffer described by metadata produced by cuDF. This has been a key operation for us to turn a table into something that we can trivially move to host or disk (spill). Because tables can be quite large, we have found that requiring them to be contiguous in memory, adds quite a bit of memory pressure and fragments the memory pool. Some tables can be GBs in size, so in order to satisfy the allocation needed for pack to return a contiguous buffer, we can actually introduce even more spill.

Lately we have been making more use of the spill framework as we are now able to retry some cuDF operations: NVIDIA/spark-rapids#7252. We would like to be able to turn cuDF tables into "spillable tables" without requiring a premeditated pack, instead performing the pack in chunks when it is actually needed. This means we want to call pack with a bounce buffer, ensuring that no large allocations happen during this process.

After the first invocation to pack, the bounce buffer contents are copied to host (where an allocation equal to the original contiguous size is waiting to be filled). We then keep calling pack iteratively, not unlike the other chunked interfaces in cuDF.

I've been working on this together with @nvdbaranec. I am going to post a series of PRs that get us there, but overall here's the plan:

• Refactor pack/unpack/metadata/contiguous_split interfaces out of copying.hpp into a new header contiguous_split.hpp: Refactor contiguous_split API into contiguous_split.hpp #13186
• Introduce a new metadata_builder that is used by the prior code, but allows us to create metadata without having to generate cudf::column to begin with: Add metadata_builder helper class #13232
• PR chunked_pack: API Implement a chunked_pack API #13260
• PR chunked_pack JNI changes: JNI api for cudf::chunked_pack #13278