pythongh-109218: Refactor tests for the complex() constructor (pythonGH-119635)

* Share common classes.
* Use exactly representable floats and exact tests.
* Check the sign of zero components.
* Remove duplicated tests (mostly left after merging int and long).
* Reorder tests in more consistent way.
* Test more error messages.
* Add tests for missed cases.

Author: serhiy-storchaka