gh-105156: Deprecate the old Py_UNICODE type in C API (#105157)

Deprecate the old Py_UNICODE and PY_UNICODE_TYPE types in the C API:
use wchar_t instead.

Replace Py_UNICODE with wchar_t in multiple C files.

Co-authored-by: Inada Naoki <songofacandy@gmail.com>

Python/modsupport.c

@@ -329,7 +329,7 @@ do_mkvalue(const char **p_format, va_list *p_va)
         case 'u':
         {
             PyObject *v;
-            Py_UNICODE *u = va_arg(*p_va, Py_UNICODE *);
+            const wchar_t *u = va_arg(*p_va, wchar_t*);
             Py_ssize_t n;
             if (**p_format == '#') {
                 ++*p_format;