Get Complex numbers to work without compromises

[Francesco Casella]

Complex numbers are increasingly used in Modelica, mainly for electrical system simulation. They are supported by OMC, but there are still three pending issues that prevent their unrestricted use. To my understanding, they should be very easy to fix. It would be nice to have them in 1.12.0.

• Wrong code generation for complex numbers in algorithms, see #4055. This requires a fix in the code generation template handling assignment of indexed array of complex or record on left hand side in an assignment.

• Various issues when handling complex equations, see #4157 and #4354. I guess that the solution suggested in #4354, namely transforming equations involving records with two real components into pairs of real equations (which is trivial) and then allowing further symbolic manipulation should automatically fix them

• Sum of complex numbers is not supported, see #4297. This impacts some models in the MSL. Shouldn't be hard to fix either.

Can we try to get this into 1.12.0?