gh-95913: Copyedit, xref and organize enum section (#98295)

* Whatsnew: Convert literals in enum section to actual x-references

* Whatsnew: Rewrite enum section for clear and consistant phrasing

* Whatsnew: Combine directly related enum items instead of seperating them

* gh-98250: Describe __str__/__format__ changes more clearly/accurately

* Tweak enum section language per feedback from Ethan