Update to new CasADi Jacobian sparsity interface

[nickbianco]

CasADi changed how the Jacobian sparsity needs to be provided in a recent version (summarized in this issue). In order to update to the most recent version of CasADi (i.e., in order to use the new FATROP solver), we will need to use this interface.

[aymanhab]

Good job digging into this @nickbianco, let me know if you need help upgrading or building

[nickbianco]

I have a working fix on this branch: https://github.com/opensim-org/opensim-core/tree/update_casadi_sparsity_detection.

I'll clean it up and make a PR soon.