bpo-29240: Fix locale encodings in UTF-8 Mode (#5170)

Modify locale.localeconv(), time.tzname, os.strerror() and other
functions to ignore the UTF-8 Mode: always use the current locale
encoding.

Changes:

* Add _Py_DecodeLocaleEx() and _Py_EncodeLocaleEx(). On decoding or
  encoding error, they return the position of the error and an error
  message which are used to raise Unicode errors in
  PyUnicode_DecodeLocale() and PyUnicode_EncodeLocale().
* Replace _Py_DecodeCurrentLocale() with _Py_DecodeLocaleEx().
* PyUnicode_DecodeLocale() now uses _Py_DecodeLocaleEx() for all
  cases, especially for the strict error handler.
* Add _Py_DecodeUTF8Ex(): return more information on decoding error
  and supports the strict error handler.
* Rename _Py_EncodeUTF8_surrogateescape() to _Py_EncodeUTF8Ex().
* Replace _Py_EncodeCurrentLocale() with _Py_EncodeLocaleEx().
* Ignore the UTF-8 mode to encode/decode localeconv(), strerror()
  and time zone name.
* Remove PyUnicode_DecodeLocale(), PyUnicode_DecodeLocaleAndSize()
  and PyUnicode_EncodeLocale() now ignore the UTF-8 mode: always use
  the "current" locale.
* Remove _PyUnicode_DecodeCurrentLocale(),
  _PyUnicode_DecodeCurrentLocaleAndSize() and
  _PyUnicode_EncodeCurrentLocale().

Include/fileutils.h

@@ -20,18 +20,41 @@ PyAPI_FUNC(char*) _Py_EncodeLocaleRaw(
 #endif
 
 #ifdef Py_BUILD_CORE
-PyAPI_FUNC(wchar_t*) _Py_DecodeUTF8_surrogateescape(
-    const char *s,
-    Py_ssize_t size,
-    size_t *p_wlen);
-
-PyAPI_FUNC(wchar_t *) _Py_DecodeCurrentLocale(
+PyAPI_FUNC(int) _Py_DecodeUTF8Ex(
     const char *arg,
-    size_t *size);
+    Py_ssize_t arglen,
+    wchar_t **wstr,
+    size_t *wlen,
+    const char **reason,
+    int surrogateescape);
 
-PyAPI_FUNC(char*) _Py_EncodeCurrentLocale(
+PyAPI_FUNC(int) _Py_EncodeUTF8Ex(
     const wchar_t *text,
-    size_t *error_pos);
+    char **str,
+    size_t *error_pos,
+    const char **reason,
+    int raw_malloc,
+    int surrogateescape);
+
+PyAPI_FUNC(wchar_t*) _Py_DecodeUTF8_surrogateescape(
+    const char *arg,
+    Py_ssize_t arglen);
+
+PyAPI_FUNC(int) _Py_DecodeLocaleEx(
+    const char *arg,
+    wchar_t **wstr,
+    size_t *wlen,
+    const char **reason,
+    int current_locale,
+    int surrogateescape);
+
+PyAPI_FUNC(int) _Py_EncodeLocaleEx(
+    const wchar_t *text,
+    char **str,
+    size_t *error_pos,
+    const char **reason,
+    int current_locale,
+    int surrogateescape);
 #endif
 
 #ifndef Py_LIMITED_API