[TASK] Use SelectItem in SelectItemProcessor

A small step towards streamlining Core code to use
the recently introduced SelectItem API.

Resolves: #101745
Releases: main
Change-Id: Ib54abeee5b09b517e84baf7c7cb115bdb9a87295
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/80665


Reviewed-by: Nikita Hovratov <nikita.h@live.de>
Tested-by: core-ci <typo3@b13.com>
Tested-by: Georg Ringer <georg.ringer@gmail.com>
Reviewed-by: Stefan B�rk <stefan@buerk.tech>
Tested-by: Stefan B�rk <stefan@buerk.tech>
Tested-by: Nikita Hovratov <nikita.h@live.de>
Reviewed-by: Georg Ringer <georg.ringer@gmail.com>