Implement Python drop_duplicates with cudf::stable_distinct.

[brandon-b-miller]

Depends on #13392.

Closes #11638
Closes #12449
Closes #11230
Closes #5286

This PR re-implements Python's DataFrame.drop_duplicates / Series.drop_duplicates to use the stable_distinct algorithm.

This fixed a large number of issues with correctness (ordering the same way as pandas) and also improves performance by eliminating a sorting step.

As a consequence of changing the behavior of drop_duplicates, a lot of refactoring was needed. The drop_duplicates function was used to implement unique(), which cascaded into changes for several groupby functions, one-hot encoding, np.unique array function dispatches, and more. Those downstream functions relied on the sorting order of drop_duplicates and unique, which is not promised by pandas.

[ttnghia]

This also can resolve #5286. Closing it can be by this PR or a separate PR after we can preserve order in drop_duplicates.

[codecov]

Codecov Report

Patch coverage: 66.66% and project coverage change: +2.04 🎉

Comparison is base (209ab6e) 85.47% compared to head (a550a2e) 87.52%.

❗ Current head a550a2e differs from pull request most recent head c3a3bf7. Consider uploading reports for the commit c3a3bf7 to get more accurate results

Additional details and impacted files

@@               Coverage Diff                @@
##           branch-23.06   #11656      +/-   ##
================================================
+ Coverage         85.47%   87.52%   +2.04%     
================================================
  Files               153      133      -20     
  Lines             25006    21776    -3230     
================================================
- Hits              21375    19059    -2316     
+ Misses             3631     2717     -914     

Impacted Files	Coverage Δ
python/cudf/cudf/core/dataframe.py	93.77% <ø> (+0.29%)	⬆️
python/cudf/cudf/core/indexed_frame.py	92.03% <66.66%> (-0.68%)	⬇️

... and 114 files with indirect coverage changes

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[shwina]

Retargeted to 23.04

[mroeschke]

The changed tests and docstrings LGTM

[bdice]

I'm planning to merge this at the end of tomorrow. I'm giving it a bit of cool-down time since it's a "breaking" PR during burndown.

[bdice]

Thanks @galipremsagar for doing some additional testing of this PR. I feel confident enough to merge this. I have some follow-up work planned, so I am going to merge now and start on that follow-up work.

[bdice]

/merge