#1660 Tying point data now treated as a policy. Still have to deal with the cases where not every component of the strain tensor are interpolated (for MITC9 Q1P2 for instance) through constexpr evaluations.

#1660 Refactored tying point data in a standalone object, which will be used as a policy for the Shell operator in order to choose an interpolation rule.

#1664 Shell operator implemented for Q2 elements, after a long due rebase on master. Tying points policy needs to be added and documentation remains to be improved.

#0 Implemented some temporary outputs in the ModelInstances for the validation of the Shell operator.

#1586 Implemented tying point interpolation, Shell operator now functional but remains to be validated. Added a ModelInstance with shell elements and a sequential post processing to generate a Q2 visualization compatible with ViZiR.

#1586 Implemented tying points data (storage/API needs improvement). Coords no longer have an Interface type (some testing is required to make sure that relevant geometric quantities can still be computed correctly.)

#1586 Removed unnecessary template parameters for the hyperelasticity policy so that we only define them at the hyerelastic law level.

#1586 Moved some of the heavy computation at the Constructor level so that we only do it once and updated documentation.

#1586 Rewritten every contribution (residual/tangent) so that we can directly use reinterpolated values. Some refactoring remains to be done and some of the computations should only be done during the initialization phase.

#1586 Hyperelasticity in generalized coordinates now working. I4 is yet to be implemented (need to compute the contravariant basis). Documentation remains to be improved, as well as some refactoring of the implementation. Optimization could be done later on as well.

#1586 Computation of local matrices needed by the the Shell operator. Made one of the hyperelastic law template so that the proper invariant holder type is used (will have to be applied to all the other hyperelastic laws).

#1586 Implemented 3D metric tensors. Displacement gradient as well as the Cauchy-Green tensor are computed in generalized coordinates.

#1586 Defined the interface for the operator and introduced a test (which is supposed to fail at the moment).

#1586 Added the skeleton for the NonlinearShell operator, still needs to be instantiated in a test to check compilation. Propagated the policy for the coords system through the relevant operators (there might be issues with the additional arguments required for the invariant computations).