Rebase the Neo-Hookean material formulation

[adtzlr]

The explicit hard-coded hyperelastic material formulation could be changed to be formulated in an arbitrary (e.g. distortional part of deformation) space and the projection from the distortional part to the "full" deformation could be implemented in a similar way how ThreeFieldVariation is done now.

Pros

• easier hard-coded hyperelastic material formulations (without automatic differentiation)

Cons

• performance!?

💡 Note
➡️ Move the development of this topic to a private repo outside of FElupe. FElupe should ship some reference implementation (like the linear-elastic and the Neo-Hookean formulations) and general API's (like Material, MaterialStrain or Hyperelastic). There are also matADi and tensortrax out there and this should be enough to play with - that's it.

[adtzlr]

Now available as hyperelastic! 🎉 🎉