Use jvp instead of storing consistent tangent operators

[bleyerj]

Consistent tangent operators are currently stored as matrix-valued Quadrature functions, which requires substantial memory.
Better would be that constitutive_update returns unmaterialized C_tang in the form of Jacobian-Vector-Product (jvp) functions which must be called against a test function when forming the tangent bilinear form.
We must preserve in some way the current approach as MFront behaviors do not allow to unmaterialize the tangent operator, still there may be some room for memory improvement by not creating the tangent Quadrature functions in the first place.