[BUGFIX] Respect fallback languages in slug generation for pages

When creating a new subpage of another page, the TCA type "slug" will
automatically generate a slug for the new page which uses the title
of the parent page. When translating the page, the slug will try to get
the correct language for the parent record (if possible). This check did
previously not respect possible fallback languages for the language of
the new record. (configured in the site configuration)

Resolves: #89213
Releases: master, 9.5
Change-Id: Id0e43aba805a7d2596e2468223517241e0151676
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/61766


Tested-by: TYPO3com <noreply@typo3.com>
Tested-by: Markus Klein <markus.klein@typo3.org>
Tested-by: Benni Mack <benni@typo3.org>
Reviewed-by: Markus Klein <markus.klein@typo3.org>
Reviewed-by: Benni Mack <benni@typo3.org>