[Docs] Missing external copyright notices for code copies

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.

Code of Conduct

• I agree to follow the PSF Code of Conduct

Read the listed files under setuptools/_distutils, setuptools/_itertools.py, and setuptools/_vendor, then compare each referenced dependency with its linked upstream license and copyright information. Account for the vendored importlib_metadata and zipp copies, and consider whether upstream changes are needed; done means the relevant copied-code notices are complete and license compliance no longer requires manual research.