[TASK] Streamline usages to LanguageService

This change reduces all logic where "fallback to default
language" is outside of LanguageService, allowing
LanguageService to deal with such functionality now.

Resolves: #99587
Releases: main
Change-Id: I01717d229d5f61ef6ab67886a30b9b73ccb4e193
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/77421


Tested-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Reviewed-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Tested-by: core-ci <typo3@b13.com>
Tested-by: Stefan Bürk <stefan@buerk.tech>
Reviewed-by: Stefan Bürk <stefan@buerk.tech>