bpo-34589: C locale coercion off by default (GH-9073)

Py_Initialize() and Py_Main() cannot enable the C locale coercion
(PEP 538) anymore: it is always disabled. It can now only be enabled
by the Python program ("python3).

test_embed: get_filesystem_encoding() doesn't have to set PYTHONUTF8
nor PYTHONCOERCECLOCALE, these variables are already set in the
parent.

Programs/python.c

@@ -6,7 +6,7 @@
 int
 wmain(int argc, wchar_t **argv)
 {
-    return Py_Main(argc, argv);
+    return _Py_WindowsMain(argc, argv);
 }
 #else
 int