Support for the importlib.metadata metadata implementation

[richafrank]

enabled by pip 22.1 by default on Python 3.11 (or later)

See https://pip.pypa.io/en/stable/news/#v22-1

To fix the failing CI / Ubuntu / 3.11-dev / latest (push) row of the test matrix.

Thoughts on adding a row to the test matrix for 3.11 with _PIP_USE_IMPORTLIB_METADATA = 0 to ensure that that flag is picked up? In theory that's an implementation detail of pip itself.

xref #1607

Contributor checklist

• Provided the tests for the changes. (Existing tests already fail.)
• Assure PR title is short, clear, and good to be included in the user-oriented changelog

Maintainer checklist

• Assure one of these labels is present: backwards incompatible, feature, enhancement, deprecation, bug, dependency, docs or skip-changelog as they determine changelog listing.
• Assign the PR to an existing or new milestone for the target version (following Semantic Versioning).

[richafrank]

The remaining major failure TypeError("Message.__new__() missing 1 required positional argument: 'orig'") is because combine_install_requirements is failing to deepcopy the _metadata attribute of the InstallRequirement accumulator, which is now of type importlib.metadata._adapters.Message. A local rebase seems to confirm that this is solved by #1519.

[atugushev]

LGTM 👍

[richafrank]

(xref pypa/pip#11044)