bpo-36346: array: Don't use deprecated APIs (GH-19653)

* Py_UNICODE -> wchar_t
* Py_UNICODE -> unicode in Argument Clinic
* PyUnicode_AsUnicode -> PyUnicode_AsWideCharString
* Don't use "u#" format.

Co-authored-by: Victor Stinner <vstinner@python.org>
4 files changed