matrix::select_k: move selection and warp-sort primitives

[achirkin]

Refactor and move a set of implementations for batch-selecting top K largest/smallest values:

• Move device warp-wide primitives bitonic_sort.cuh to the public raft::util namespace, add tests.
• Create a new public matrix::select_k interface.
• Deprecate the legacy public raft::spatial::knn::select_k interface.
• Copy/adapt select_k tests.
• Move/adapt select_k benchmarks.
• Rework the internals of select_warpsort.cuh to enable more implementations.

Closes #853

[cjnolet]

rerun tests

[achirkin]

Note, this PR does not add any template specialization at this point. There are two reasons for this: (1) it's not clear to which component the specializations would belong, (2) the impact on the compile times needs to be investigated more thoroughly.

[codecov-commenter]

Codecov Report

Base: 87.99% // Head: 87.99% // No change to project coverage 👍

Coverage data is based on head (dc3043c) compared to base (0e96662).
Patch has no changes to coverable lines.

Additional details and impacted files

@@              Coverage Diff              @@
##           branch-23.02    #1085   +/-   ##
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  Coverage         87.99%   87.99%           
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  Files                21       21           
  Lines               483      483           
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  Hits                425      425           
  Misses               58       58           

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[cjnolet]

Thanks for the changes and discussions thus far. I think this is almost ready. Mostly minor things at this point.

[cjnolet]

I think we can continue the discussion to move code shared by test and bench in follow-ons in 23.04. I think this looks great for now!

[cjnolet]

/merge