[GUI.Component] Add virtualization for attachment performer

[bakpaul]

Add virtualization layer to attachment performers.

There exists two of them, either using lagrangian based constraints or springs. A common method start_partial already existed that was supposed to add required components and parametrize them to either add bilateral constraint or a spring, but this common mechanism was not link with any virtual inheritance.

I need to handle both performers blindly using this method (start_partial) so I added a virtualization layer that makes more sens than what currently exists. I use it in this PR -> (Sofa.IGTLink PR).

I've also took advantage of this refactoring to rename some attributes that where not following the naming policy, because why not.

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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).

[bakpaul]

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

[hugtalbot]

Looks good to me but a bit hard to review due to the mix of changes. It would have been easier with two separate PRs