gh-95914: Add links to 3.11 WhatsNew Summary items

[CAM-Gerlach]

The final part of #95914 , and in turn part of #95913

Add links/references for each of the Summary items in the Python 3.11 What's New document where readers can find more information. Specifically:

• For PEP-size items with their own sections, just reference the section directly and use its title as the link title, which is DRY/reduces duplication and also helps translators (per Doc: Remove title text from internal links #98409)
• For the deprecation PEPs, link the entry for each from the summary description and elide the mostly redundant PEP titles (and for PEP 594, re-order the two bullets to put the main description first)
• For ``PYTHONSAFEPATH`, link the entry and cross-reference the various entities (and make the summary a bit more concise)
• For the tomllib addition, since the What's New entry contains essentially the same information of the summary, just use the appropriate Sphinx syntax to link the PEP, module and website directly

• Issue: List and document remaining significant PEPs in What's New in 3.11 #95914

[miss-islington]

Thanks @CAM-Gerlach for the PR, and @ezio-melotti for merging it 🌮🎉.. I'm working now to backport this PR to: 3.11.
🐍🍒⛏🤖 I'm not a witch! I'm not a witch!

[bedevere-bot]

GH-98420 is a backport of this pull request to the 3.11 branch.