[REVIEW] Preprocessing out of experimental

[viclafargue]

Closes #3483.

This PR removes unnecessary thirdparty code, tests most thirdparty and adapter functions and moves preprocessing out of the experimental namespace. Preprocessing models testing will also be strengthen. Finally, the preprocessing models will keep being accessible from the experimental namespace at least for the 0.19 release.

[JohnZed]

I like the expanded tests and new namespace! Just a few suggestions and mostly questions.

[JohnZed]

@viclafargue Per other discussions, if we can get the random-generators to all use the method where the seed used is random but reported in the logs, I think this will be good to go. (Also need to fix the merge conflicts of course)

[codecov-io]

Codecov Report

Merging #3676 (83e9b9b) into branch-0.19 (fd9ec89) will increase coverage by 5.18%.
The diff coverage is n/a.

@@               Coverage Diff               @@
##           branch-0.19    #3676      +/-   ##
===============================================
+ Coverage        80.70%   85.89%   +5.18%     
===============================================
  Files              227      225       -2     
  Lines            17615    17096     -519     
===============================================
+ Hits             14217    14684     +467     
+ Misses            3398     2412     -986     

Flag	Coverage Δ
dask	49.27% <ø> (+4.28%)	⬆️
non-dask	77.80% <ø> (+4.89%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
python/cuml/__init__.py	95.58% <ø> (+0.20%)	⬆️
...cuml/_thirdparty/sklearn/preprocessing/__init__.py	100.00% <ø> (ø)
...on/cuml/_thirdparty/sklearn/preprocessing/_data.py	64.52% <ø> (+1.41%)	⬆️
...hirdparty/sklearn/preprocessing/_discretization.py	83.33% <ø> (-0.88%)	⬇️
...l/_thirdparty/sklearn/preprocessing/_imputation.py	85.54% <ø> (+22.74%)	⬆️
python/cuml/_thirdparty/sklearn/utils/extmath.py	97.22% <ø> (+40.32%)	⬆️
...cuml/_thirdparty/sklearn/utils/skl_dependencies.py	80.00% <ø> (+26.07%)	⬆️
...thon/cuml/_thirdparty/sklearn/utils/sparsefuncs.py	90.90% <ø> (+48.32%)	⬆️
...ython/cuml/_thirdparty/sklearn/utils/validation.py	64.10% <ø> (+41.65%)	⬆️
python/cuml/benchmark/algorithms.py	94.38% <ø> (ø)
... and 188 more

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[JohnZed]

I think the usages look good... would be nice if in the future we can automate a bit more so we just use the fixture and don't have to manually set the seed each time, but should be ok for release. Just want to make the small change to read seed from environment if available and then we're good to go!

[JohnZed]

One more tiny thing - can you add a row for preprocessing to the list of algorithms in the README? We don't need to list all of them, just something like:

Preprocessing | Scikit-learn compatible preprocessing including imputation, normalization, etc. |

[viclafargue]

Thanks for the review. @lowener has some changes that would be interesting to add to this PR before merging it. @lowener changes are now merged. Changes are visible here.

[JohnZed]

Looks great! Thank you for the additional test too, @lowener

[JohnZed]

@gpucibot merge