[Docs] Missing external copyright notices for code copies

[stefan6419846]

Summary

When looking through the code, there seem to be some code copies with incomplete original copyright information:

• https://github.com/pypa/setuptools/blob/main/setuptools/_distutils/compat/py39.py has references to undisclosed versions of more-itertools. Its MIT license requires keeping the original copyright notice.
• https://github.com/pypa/setuptools/blob/main/setuptools/_itertools.py has a reference to jaraco.itertools 6.1 and missing the original copyright notice as well (https://github.com/jaraco/jaraco.itertools/blob/v6.1.0/LICENSE).

Further references in the vendored dependencies:

• https://github.com/pypa/setuptools/blob/main/setuptools/_vendor/importlib_metadata/_collections.py references jaraco.collections 3.3
• https://github.com/pypa/setuptools/blob/main/setuptools/_vendor/importlib_metadata/_functools.py references jaraco.functools 3.3
• https://github.com/pypa/setuptools/blob/main/setuptools/_vendor/importlib_metadata/_itertools.py references more-itertools 8.8
• https://github.com/pypa/setuptools/blob/main/setuptools/_vendor/importlib_metadata/_text.py references jaraco.text 3.5
• https://github.com/pypa/setuptools/blob/main/setuptools/_vendor/zipp/compat/py313.py references jaraco.functools 4.1
• https://github.com/pypa/setuptools/blob/main/setuptools/_vendor/zipp/_functools.py references jaraco.functools 4.0.2

While I am aware that the vendored dependencies might need external changes, they are - AFAIK - all maintained by Jason, as for setuptools as well. To keep discussions about this in one place, I refrained from opening dedicated issues in each repository for now.

OS / Environment

No response

Additional Information

It simplifies license compliance handling. At the moment, such references have to be researched and resolved manually, while fixing this upstream would benefit all users.

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