do sensitivity calculations for processed variables in C++

[martinjrobins]

We have existing C++ code to calculate sensitivities for derived variables (this is used if output_variables is set). Once #4545 is complete, we will be able to take the output from the IDAKLU sensitivity solve and use this C++ code to calculate the output sensitivities in the Solution class.

Motivation

Efficiency, should be faster than the current implementation

Implementation

• Wrap C++ sensitivity code
• We used to rearrange the IDAKLU sensitivity output to match that of the casadi solver, once remove explicit sensitivity calculation (casadi solver) #4545 is done this can be removed
• Replace sensitivity calculation in the Solution class with the wrapped C++ code

[martinjrobins]

Related to #3910