bpo-35883: Py_DecodeLocale() escapes invalid Unicode characters

[vstinner]

Python no longer fails at startup with a fatal error if a command
line argument contains an invalid Unicode character.

The Py_DecodeLocale() function now escapes byte sequences which would
be decoded as Unicode characters outside the [U+0000; U+10ffff]
range.

Use MAX_UNICODE constant in unicodeobject.c.

https://bugs.python.org/issue35883

[miss-islington]

Thanks @vstinner for the PR 🌮🎉.. I'm working now to backport this PR to: 3.8, 3.9.
🐍🍒⛏🤖

[bedevere-bot]

GH-24905 is a backport of this pull request to the 3.9 branch.

[bedevere-bot]

GH-24906 is a backport of this pull request to the 3.8 branch.

[bedevere-bot]

⚠️⚠️⚠️ Buildbot failure ⚠️⚠️⚠️

Hi! The buildbot aarch64 RHEL8 3.9 has failed when building commit aa967ec.

What do you need to do:

1. Don't panic.
2. Check the buildbot page in the devguide if you don't know what the buildbots are or how they work.
3. Go to the page of the buildbot that failed (https://buildbot.python.org/all/#builders/41/builds/279) and take a look at the build logs.
4. Check if the failure is related to this commit (aa967ec) or if it is a false positive.
5. If the failure is related to this commit, please, reflect that on the issue and make a new Pull Request with a fix.

You can take a look at the buildbot page here:

https://buildbot.python.org/all/#builders/41/builds/279

Summary of the results of the build (if available):

== Tests result: ENV CHANGED ==

411 tests OK.

10 slowest tests:

• test_concurrent_futures: 3 min 56 sec
• test_capi: 3 min 13 sec
• test_peg_generator: 3 min 4 sec
• test_unparse: 2 min 59 sec
• test_tokenize: 2 min 46 sec
• test_multiprocessing_spawn: 2 min 23 sec
• test_asyncio: 2 min 14 sec
• test_gdb: 2 min 10 sec
• test_lib2to3: 2 min 2 sec
• test_multiprocessing_forkserver: 1 min 27 sec

1 test altered the execution environment:
test_asyncio

13 tests skipped:
test_devpoll test_ioctl test_kqueue test_msilib test_ossaudiodev
test_startfile test_tix test_tk test_ttk_guionly test_winconsoleio
test_winreg test_winsound test_zipfile64

Total duration: 6 min 5 sec

Click to see traceback logs

Traceback (most recent call last):
  File "/home/buildbot/buildarea/3.9.cstratak-RHEL8-aarch64/build/Lib/asyncio/sslproto.py", line 321, in __del__
    self.close()
  File "/home/buildbot/buildarea/3.9.cstratak-RHEL8-aarch64/build/Lib/asyncio/sslproto.py", line 316, in close
    self._ssl_protocol._start_shutdown()
  File "/home/buildbot/buildarea/3.9.cstratak-RHEL8-aarch64/build/Lib/asyncio/sslproto.py", line 590, in _start_shutdown
    self._abort()
  File "/home/buildbot/buildarea/3.9.cstratak-RHEL8-aarch64/build/Lib/asyncio/sslproto.py", line 731, in _abort
    self._transport.abort()
  File "/home/buildbot/buildarea/3.9.cstratak-RHEL8-aarch64/build/Lib/asyncio/selector_events.py", line 680, in abort
    self._force_close(None)
  File "/home/buildbot/buildarea/3.9.cstratak-RHEL8-aarch64/build/Lib/asyncio/selector_events.py", line 731, in _force_close
    self._loop.call_soon(self._call_connection_lost, exc)
  File "/home/buildbot/buildarea/3.9.cstratak-RHEL8-aarch64/build/Lib/asyncio/base_events.py", line 746, in call_soon
    self._check_closed()
  File "/home/buildbot/buildarea/3.9.cstratak-RHEL8-aarch64/build/Lib/asyncio/base_events.py", line 510, in _check_closed
    raise RuntimeError('Event loop is closed')
RuntimeError: Event loop is closed