[DOCS] Enhance changelogs around enums

Links to the official PHP documentation for enums have been added
to ease access for developers who do not know this feature yet.

Additionally, in the Enumeration deprecation changelog a link
to the feature "Let Extbase handle native enums" has been added.

Resolves: #102719
Related: #101163
Related: #101396
Releases: main
Change-Id: I2188e1308a797fa827e646a31372e0a018a9d607
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/82279


Tested-by: Stefan Bürk <stefan@buerk.tech>
Reviewed-by: Stefan Bürk <stefan@buerk.tech>
Tested-by: core-ci <typo3@b13.com>
Tested-by: Garvin Hicking <gh@faktor-e.de>
Reviewed-by: Garvin Hicking <gh@faktor-e.de>
Reviewed-by: Oliver Klee <typo3-coding@oliverklee.de>