Enable complex CI coeff optimization

CI coefficients could be complex, and therefore we should be able to optimize both the real and imaginary parts of the coefficients.

As the code currently stands, we only optimize the real part of any ValueType parameter. In #4819, we are moving the VariableSet to be purely real, so it is the responsibility of the wavefunction component to register the real and imaginary components of a complex parameter as two reals to VariableSet. This is being implemented for RotatedSPOs and should be fixed for CI coefficients as well.