add option to compute jacobian determinants

[j042]

det(jacobian) is as interesting as jacobian matrix sometimes and it would be nice to have an option to have them returned together. In case J doesn't have a square shape, we could either return its weight or error.

[jzwar]

Related to FFD improvements :
https://github.com/tataratat/gustaf/discussions/108

[jzwar]

I think, creating a new function in SplineBase, (pure python) that can compute the geometric_measure would also be a good first task for students. Maybe @FSchwar would be interested? @j042 would you mind coordinating while I am on vacation?

[j042]

sure