[SofaTest] ADD a PrintTo method so test failure shows human readable informations.

[damienmarchal]

But default google test prints raw values when the tests cases are provided by GetParams.
By adding a PrintTo function this behavior can be changed so that custom types are easier
to read.

In the PR i adds a PrintTo for the Python_test_data object.

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• builds with SUCCESS for all platforms on the CI.
• does not generate new warnings.
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• does not generate new scene test failures.
• does not break API compatibility.
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