Add stdlib_deprecations module

[vstinner]

Following Formalize the concept of “soft deprecation” (don’t schedule removal) in PEP 387 “Backwards Compatibility Policy” discussion and my PEP PR PEP 387: Add Soft Deprecation section, I propose to add a new stdlib_deprecations module which provides an API for linters to check if an API is deprecated or not.

Linked PRs

• gh-106240: Add stdlib_deprecations module #106241

[JelleZijlstra]

Note that any new stdlib module requires a PEP: https://peps.python.org/pep-0002/#acceptance-procedure

[vstinner]

Closed: see #106241 (comment)