New Issue: Math module - add overload of 'sgn' for complex numbers

19165, "lydia-duncan", "Math module - add overload of 'sgn' for complex numbers", "2022-02-02T22:46:23Z"

Damian points out that ISO 80000-2 specifies a version for integers, reals, and complexes. It looks like we only support integers and reals. This is not a 2.0 task, but it might be nice to add an overload that supports complexes.

In recording this, I did not look at whether C provides an overload for complexes. But, since we don't rely on C implementations for the other sgn overloads, I don't think that will be a problem.