[SofaCore] Merge TData in Data.

[damienmarchal]

I don't know what exactly was TData for, but in years no-one ever use it so I merged Data & TData to make things more clear.
I also re-implemented the existing feature using the child-delegation pattern instead of relying on call super.

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Reviewers will merge this pull-request only if

• it builds with SUCCESS for all platforms on the CI.
• it does not generate new warnings.
• it does not generate new unit test failures.
• it does not generate new scene test failures.
• it does not break API compatibility.
• it is more than 1 week old (or has fast-merge label).

[epernod]

[ci-build][with-all-tests]

[damienmarchal]

Thanks you very much @epernod for the review.

[hugtalbot]

PR looks fine, but we absolutely need to define the convention about _doXXX_ or _isXXXX_
This should be definitely generalized within the whole code base AND the guidelines of SOFA.

[damienmarchal]

So ready, isn it :)

[damienmarchal]

So after discussion on gitter, the convention is
"each time you use the Template Method design pattern which delegate to its child private implementation then you must use the double _ to indicate it".
https://isocpp.org/wiki/faq/strange-inheritance#private-virtuals

If it is not private then feel free (which is exactly how is the sofa code base right now).

[damienmarchal]

Appart from that, I did a quick search in the sofa code base, I didn't paid attention to how much of the doXXXX stuff are with a public visibility... which is clearly not what the design pattern suggested initially.