[FOLLOWUP][TASK] Unify TypoScript-related helper methods

Now the TypoScriptService is PHP strict we need to take care
the processed value is of the correct type.


Resolves: #78650
Releases: master
Change-Id: I1d79059c65676ce2e8126b6502c822d8b500379e
Reviewed-on: https://review.typo3.org/52252


Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Tested-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Reviewed-by: Georg Ringer <georg.ringer@gmail.com>
Tested-by: Georg Ringer <georg.ringer@gmail.com>