[BUGFIX] Harmonize page ids in Record List search

The list of ids generated by `getSearchableWebmounts()` may contain
duplicated values being passed into an `IN()` criteria, causing
additional load to the database server.

The values are now de-duplicated by applying `array_unique()` onto the
list before passing the list around.

Resolves: #100750
Releases: main, 11.5
Change-Id: Ib49bf1a5903cca2fbaa12ea240050caa7908f69c
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/78874


Tested-by: core-ci <typo3@b13.com>
Tested-by: Andreas Fernandez <a.fernandez@scripting-base.de>
Reviewed-by: Andreas Fernandez <a.fernandez@scripting-base.de>
Reviewed-by: Oliver Klee <typo3-coding@oliverklee.de>