Enh: deprecate legacy plots and code

[arshiaar]

Overview

Part of #3156

Description of the changes proposed in this pull request:

• Added deprecation decorators using sklearn deprecated since its an existing dependency.
• Decorators added to: bar_legacy, summary_legacy, dependence_legacy, waterfall_legacy
• Added unit tests for dependence_legacy, summary_legacy, and waterfall_legacy.
• Added decorator for kmeans in utils/._legacy.py

Potentially could create own decorator using the python warnings module.
Did not include unit tests for bar_legacy as function is breaking outside of decorator.

Checklist

• All pre-commit checks pass.
• Unit tests added (if fixing a bug or adding a new feature)

[dsgibbons]

Maybe update the message to say something like "will be removed in 0.44"?

[codecov]

Codecov Report

Patch coverage: 100.00% and project coverage change: +0.11% 🎉

Comparison is base (3bd5d66) 57.58% compared to head (2665dc4) 57.70%.
Report is 5 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3209      +/-   ##
==========================================
+ Coverage   57.58%   57.70%   +0.11%     
==========================================
  Files          88       88              
  Lines       12511    12521      +10     
==========================================
+ Hits         7205     7225      +20     
+ Misses       5306     5296      -10     

Files Changed	Coverage Δ
shap/plots/_bar.py	60.36% <100.00%> (+0.36%)	⬆️
shap/plots/_beeswarm.py	79.69% <100.00%> (+1.43%)	⬆️
shap/plots/_scatter.py	48.43% <100.00%> (+0.23%)	⬆️
shap/plots/_waterfall.py	86.11% <100.00%> (+0.08%)	⬆️
shap/utils/_legacy.py	87.57% <100.00%> (+0.14%)	⬆️

... and 2 files with indirect coverage changes

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[thatlittleboy]

Few suggestions (up for discussion, except the last one):

• Use the phrase "marked for deprecation" instead of "deprecated". I've always found it confusing myself, but maybe it's just me.
• Maybe shap v0.43.0 instead of Version 0.43.0. I'm thinking to specify "shap" because there might be wrapper libraries around shap, and I'm afraid end users will confuse 0.43 for the wrapper library's version rather than shap's.
• Mention what the alternative should be. "Please use shap.plots.bar instead" or words to that effect. For summary_legacy, maybe just nudge the user towards using the dedicated shap.plots functions.
• The docstrings of the legacy functions should be updated as well with the deprecation message & reference to the suggested alternative, in a deprecation admonition / warning box.