_PyCoreConfig_Read() is now responsible to choose the filesystem
encoding and error handler. Using Py_Main(), the encoding is now
chosen even before calling Py_Initialize().

_PyCoreConfig.filesystem_encoding is now the reference, instead of
Py_FileSystemDefaultEncoding, for the Python filesystem encoding.

Changes:

* Add filesystem_encoding and filesystem_errors to _PyCoreConfig
* _PyCoreConfig_Read() now reads the locale encoding for the file
  system encoding.
* PyUnicode_EncodeFSDefault() and PyUnicode_DecodeFSDefaultAndSize()
  now use the interpreter configuration rather than
  Py_FileSystemDefaultEncoding and Py_FileSystemDefaultEncodeErrors
  global configuration variables.
* Add _Py_SetFileSystemEncoding() and _Py_ClearFileSystemEncoding()
  private functions to only modify Py_FileSystemDefaultEncoding and
  Py_FileSystemDefaultEncodeErrors in coreconfig.c.
* _Py_CoerceLegacyLocale() now takes an int rather than
  _PyCoreConfig for the warning.

* Add stdio_encoding and stdio_errors fields to _PyCoreConfig.
* Add unit tests on stdio_encoding and stdio_errors.

On Windows, the LC_CTYPE is now set to the user preferred locale at
startup: _Py_SetLocaleFromEnv(LC_CTYPE) is now called during the
Python initialization. Previously, the LC_CTYPE locale was "C" at
startup, but changed when calling setlocale(LC_CTYPE, "") or
setlocale(LC_ALL, "").

pymain_read_conf() now also calls _Py_SetLocaleFromEnv(LC_CTYPE) to
behave as _Py_InitializeCore(). Moreover, it doesn't save/restore the
LC_ALL anymore.

On Windows, standard streams like sys.stdout now always use
surrogateescape error handler by default (ignore the locale).

Standard streams like sys.stdout now use the "surrogateescape" error
handler, instead of "strict", on the POSIX locale (when the C locale is not
coerced and the UTF-8 Mode is disabled).

Add tests on sys.stdout.errors with LC_ALL=POSIX.

* Move Py_SetStandardStreamEncoding() from pylifecycle.c
  to coreconfig.c
* Add _Py_ClearStandardStreamEncoding() private function.
* pymain_free() now calls _Py_ClearStandardStreamEncoding().
* Add assertions add the end of _PyCoreConfig_Read()
* _PyCoreConfig_Copy(): rename COPY_STR_ATTR() macro
  to COPY_WSTR_ATTR().
* Fix get_stdio_errors() indentation.

* _Py_InitializeCore() now sets the LC_CTYPE locale to the user
  preferred locale before checking if the C locale should be coerced
  or not in _PyCoreConfig_Read().
* Fix pymain_read_conf(): remember if the C locale has been coerced
  when the configuration should be read again if the encoding has
  changed.

Python now gets the locale encoding with C code to initialize the encoding
of standard streams like sys.stdout. Moreover, the encoding is now
initialized to the Python codec name to get a normalized encoding name and
to ensure that the codec is loaded. The change avoids importing
_bootlocale and _locale modules at startup by default.

When the PYTHONIOENCODING environment variable only contains an encoding,
the error handler is now is now set explicitly to "strict".

Rename also get_default_standard_stream_error_handler() to
get_stdio_errors().

Reduce the buffer to format the "cpXXX" string (Windows locale encoding).

On HP-UX with C or POSIX locale, sys.getfilesystemencoding() now returns
"ascii" instead of "roman8" (when the UTF-8 Mode is disabled and the C locale
is not coerced).

nl_langinfo(CODESET) announces "roman8" whereas it uses the Latin1
encoding in practice.

* The UTF-8 Mode is now also enabled by the "POSIX" locale, not only
  by the "C" locale.
* On FreeBSD, Py_DecodeLocale() and Py_EncodeLocale() now also forces
  the ASCII encoding if the LC_CTYPE locale is "POSIX", not only if
  the LC_CTYPE locale is "C".
* test_utf8_mode.test_cmd_line() checks also that the command line
  arguments are decoded from UTF-8 when the the UTF-8 Mode is enabled
  with POSIX locale or C locale.

Robust caching of calculated properties is
harder than it looks at first glance, so add
a solid, well-tested implementation to the
standard library.

AIX uses ISO-8859-1 encoding for the C locale.

Remove "trace.cover" left from previous test runs before testing
that it is no longer created.

bpo-32968: Make modulo and floor division involving Fraction and float consistent with other operations (#5956)

Make mixed-type `%` and `//` operations involving `Fraction` and `float` objects behave like all other mixed-type arithmetic operations: first the `Fraction` object is converted to a `float`, then the `float` operation is performed as normal. This fixes some surprising corner cases, like `Fraction('1/3') % inf` giving a NaN.

Thanks Elias Zamaria for the patch.

An old apparent AIX behavior workaround in test_subprocess's
test_undecodable_env is no longer needed.

Reported by Svace static analyzer.

Reported by Svace static analyzer.

Previously marks stack was upsized even there was space for additional item.

`yield conn`, instead of just `yield`.

Avoids an integer underflow in the time module's year handling code.

bpo-34492: Python/coreconfig.c: Add missing NULL check to _Py_wstrlist_copy().

Fix _Py_wstrlist_clear() call on a wrong list.

Reported by Svace static analyzer.

Reported by Svace static analyzer.

Also, propagate the error from PyNumber_AsSsize_t() because we don't care
only about OverflowError which is not reported if the second argument is NULL.

Reported by Svace static analyzer.

Reported by Svace static analyzer.

Reported by Svace static analyzer.