[TASK] Modernize array function callbacks in Fluid

Function callbacks are declared using the new PHP 8.1 feature
"first class callable", which e.g. uses the named `trim(...)`
function symbol, instead of the string `'trim'`.

see https://www.php.net/manual/en/functions.first_class_callable_syntax.php

Resolves: #100147
Releases: main
Change-Id: Id4577fb5412163f5e49927f2f404f21d82a8e9e1
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/78100


Reviewed-by: Benni Mack <benni@typo3.org>
Tested-by: Torben Hansen <derhansen@gmail.com>
Tested-by: Benni Mack <benni@typo3.org>
Reviewed-by: Torben Hansen <derhansen@gmail.com>
Tested-by: core-ci <typo3@b13.com>