[TASK] Remove fallback in SiteConfiguration constructor

Its todo is solved. This also introduces constructor property promotion.

Resolves: #101213
Releases: main
Change-Id: I929bd9584e9f83c92919973a2769b0cccd55d9b4
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/79574


Reviewed-by: Stefan Bürk <stefan@buerk.tech>
Tested-by: Benni Mack <benni@typo3.org>
Tested-by: Stefan Bürk <stefan@buerk.tech>
Tested-by: core-ci <typo3@b13.com>
Reviewed-by: Benni Mack <benni@typo3.org>
Reviewed-by: Oliver Klee <typo3-coding@oliverklee.de>