[SofaDistanceGrid] Improve DistanceGrid current code or re-implement the component

[epernod]

[th-skam]

• Use of raw pointers in various places within the code that could be converted to smart pointers.
• Custom mechanism with a count block for sharing raw pointers-to-the-distance-grid between the collision model and the collision elements:
  https://github.com/sofa-framework/sofa/blob/1eb5242037be574a278b3b6621674a94fd7b8aa3/applications/plugins/SofaDistanceGrid/src/SofaDistanceGrid/DistanceGrid.cpp#L105-L118
  https://github.com/sofa-framework/sofa/blob/1eb5242037be574a278b3b6621674a94fd7b8aa3/applications/plugins/SofaDistanceGrid/src/SofaDistanceGrid/DistanceGrid.cpp#L1238-L1258
  Why not switch to std::shared_ptr?

[epernod]

most probably because this code is older than the official introduction of shared_ptr in the STL 😱