[objectmodel] Avoid extra copy in DataFileNameVector

[alxbilger]

trafficstars

And also clean DataFileName and DataFileNameVector.

DataFileNameVector has been extracted in its own files.

The extra copy came from the DataFileNameVector constructor which took a sofa::type::vector<std::string> but it should take a sofa::type::SVector<std::string>. Therefore, there was an implicit conversion.

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[fredroy]

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

[hugtalbot]

Sorry @alxbilger conflict occurred ! :+1: for the cleaning!