[3.11] gh-135034: Normalize link targets in tarfile, add `os.path.realpath(strict='allow_missing')` (GH-135037) (GH-135068)

Addresses CVEs 2024-12718, 2025-4138, 2025-4330, and 2025-4517.
(cherry picked from commit 3612d8f51741b11f36f8fb0494d79086bac9390a)
(cherry picked from commit c358142cab7ce621a2745262a90df967b357f61c)

Co-authored-by: Łukasz Langa <lukasz@langa.pl>
Signed-off-by: Łukasz Langa <lukasz@langa.pl>
Co-authored-by: Petr Viktorin <encukou@gmail.com>
Co-authored-by: Seth Michael Larson <seth@python.org>
Co-authored-by: Adam Turner <9087854+AA-Turner@users.noreply.github.com>
Co-authored-by: Serhiy Storchaka <storchaka@gmail.com>

• Doc/library/os.path.rst[diff]
• Doc/library/tarfile.rst[diff]
• Doc/whatsnew/3.11.rst[diff]
• Lib/genericpath.py[diff]
• Lib/ntpath.py[diff]
• Lib/posixpath.py[diff]
• Lib/tarfile.py[diff]
• Lib/test/test_ntpath.py[diff]
• Lib/test/test_posixpath.py[diff]
• Lib/test/test_tarfile.py[diff]
• Misc/NEWS.d/next/Security/2025-06-02-11-32-23.gh-issue-135034.RLGjbp.rst[Added - diff]