[Mapping] Add distance to plane mapping

[bakpaul]

Add new linear mapping computing a distance to a plane. The idea is to then use it to apply constraints to stay on a plane for instance (what some might call sliding constraints) or contact. The contact part is currently more tricky because there is no current way to simply add UnilateralLagrangianConstraint to a mstate --> a PR doing this will come in the future.

Parametrization is simple : a normal and a random point on the plane (used ton compute the distance to the origin. Actually only a scalar might have been sufficient, but it is easier to compute a point respecting this with the distance in mind rather than the distance with a random point, even if it is just a scalar product)

Added scene test + extensive unit testing

Will only work in position for rigid.

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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.
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[hugtalbot]

Nice ! I will give a try to the example scene.
Even better would be an associated doc page .. 👼

[fredroy]

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