bpo-29240: Ignore UTF-8 Mode in time module (#5148)

time.strftime() must use the current LC_CTYPE encoding, not UTF-8
if the UTF-8 mode is enabled.

Add _PyUnicode_DecodeCurrentLocale() function.

Objects/unicodeobject.c

@@ -3836,6 +3836,12 @@ _PyUnicode_DecodeCurrentLocaleAndSize(const char *str, Py_ssize_t len,
     return unicode_decode_locale(str, len, errors, 1);
 }
 
+PyObject*
+_PyUnicode_DecodeCurrentLocale(const char *str, const char *errors)
+{
+    return unicode_decode_locale(str, (Py_ssize_t)strlen(str), errors, 1);
+}
+
 PyObject*
 PyUnicode_DecodeLocale(const char *str, const char *errors)
 {