[R] Export function xgb.shap.data

[hcho3]

https://discuss.xgboost.ai/t/xgb-shap-data-not-found/2557?u=hcho3

Even though the utility function xgb.shap.data was visible in the R-package documentation (here), it was not explicitly published from NAMESPACE. The function should be exported so that it can be actually used.

[trivialfis]

Does the user actually need to call that function in order to use SHAP related features? Just curious since it's a new public API function.

[hcho3]

@trivialfis It's supposed to be an internal function, but for some reason it is already part of the public documentation.
https://www.rdocumentation.org/packages/xgboost/versions/1.5.0.2/topics/xgb.shap.data
https://www.rdocumentation.org/packages/xgboost/versions/1.4.1.1/topics/xgb.shap.data
https://www.rdocumentation.org/packages/xgboost/versions/1.3.2.1/topics/xgb.shap.data

[trivialfis]

If no one can use it, let's remove the public document instead. ;-)

[trivialfis]

I will leave it for you to decide. I'm not familiar with R so I worried about a new function to maintain. If you think it's best to export the function then this PR looks good to me.

[hcho3]

Closing this, as xgb.shap.data was marked as internal in #6374, and the document has been regenerated. https://github.com/dmlc/xgboost/blob/master/R-package/man/xgb.plot.shap.Rd no longer shows xgb.shap.data