Missing documentation for RooChi2Var since ROOT 6.36

[AlkaidCheng]

Explain what you would like to see improved and how.

It seems that for some reason the documentation page for RooChi2Var (which gives the definition of RooAbsReal::createChi2 has been missing since ROOT 6.36. The documentation is still available in ROOT 6.34. I checked that the source code still exists (and being used) in the same place for 6.36+.

It would also help to direct user to this documentation when checking the definition of createChi2.

ROOT version

6.36+

Installation method

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Operating system

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Additional context

No response

[guitargeek]

Thanks. Your are right. The definition of RooChi2Var was hidden on purpose because it's an implementation detail of createChi2, in fact the whole class was removed from the public user interface. But I need to move the relevant docs to the docstring of createChi2