rename shap-related explainability to sklearn

[dennisbader]

Checklist before merging this PR:

• Mentioned all issues that this PR fixes or addresses.
• Summarized the updates of this PR under Summary.
• Added an entry under Unreleased in the Changelog.

Summary

Part 2 of splitting #3049 into multiple PRs.

• Renames ShapExplainer to SKLearnExplainer to better reflect its scope of explaining sklearn-based models.
• Renames ShapExplainabilityResult to SHAPExplainabilityResult to better reflect SHAP-based explainability results.

[review-notebook-app]

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Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 96.24%. Comparing base (8a834c8) to head (38847e7).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3103      +/-   ##
==========================================
- Coverage   96.31%   96.24%   -0.07%     
==========================================
  Files         161      161              
  Lines       17350    17350              
==========================================
- Hits        16710    16699      -11     
- Misses        640      651      +11     

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[daidahao]

Thank you again! @dennisbader