[TASK] Streamline LinkValidatorController

Refactoring of ext:linkvalidator backend controller
towards new backend templating strategy together
with a series of details to simplify code.

Resolves: #96779
Related: #96730
Releases: main
Change-Id: I347e7f167ac98cbd13a1fdb64122c1a99b7c9756
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/73349


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