Disable PEP 658 for the legacy resolver

The first entry in the bug fixes section for the 23.2 release's
changelog incorrectly listed the the PR/Issue for "Fix pip 
completion --zsh" as #11416. However, the PR that fixed this
issue was actually #11417. This commit fixes this oversight/off by one error so that the changelog points to the correct PR.

Release 23.2

Ensure requirements are prepared before get_dist()

The legacy resolver seems to prepare requirements differently that can
leave them half-done in certain code paths. I'm not quite sure how it's
doing things, but at least we can do this to make sure they do things
right.

Update vendored urllib3 from 1.26.15 to 1.26.16

Vendoring updates for 23.2

Co-authored-by: NTzu-ping Chung <uranusjr@gmail.com>

This makes it possible to test both branches on any Python version.

Due to the advent of build isolation, it is no longer necessary to install
setuptools and wheel in an environment just to install other packages.
Moreover, on Python 3.12 both ensurepip [1] and virtualenv [2] are to stop
installing setuptools & wheel by default. This means that when those packages
are present in a Python 3.12+ environment, it is reasonable to assume that
they are runtime dependencies of the user's project, and therefore should be
included in freeze output.

distribute is just obsolete.

[1] https://github.com/python/cpython/issues/95299
[2] https://github.com/pypa/virtualenv/pull/2558

Surface LegacyVersion and LegacySpecifier deprecation warnings

Record download of completed partial requirements

Pass revisions options explicitly to mercurial commands