No computation of metric associated to geometric approximation at PARBDY surface points

[Algiane]

Try to not compute / modify the metric associated to geometric approximation for MG_PARBDY points (points along partition interfaces in ParMmg). On such points:

• we want to preserve sizes and directions of input metric (so we don't want to force anisotropic metrics to be aligned with tangent plane and normal directions as it is done by the geometric approximation)
• As MG_PARBDY entities are required and doen't represent a real surface we don't care about the geometric approximation.