MATLAB/Octave: Modernize 3D curvilinear operators (grad3DCurv / div3DCurv / jacobian3D)

[jcorbino]

Follow-up to #312, which modernizes the 2D curvilinear operators. The 3D counterparts on main still have the same architectural limitations.

[github-actions]

This issue has had no activity for 25 days. It will be marked stale in 3 days if there is no further activity.

[github-actions]

Thanks for the discussion and work here. This issue has had no activity for 28 days, so it is now marked stale. If there is no further activity, it will be closed in 42 days.