[TASK] Simplify Frontend Request Handler

This patch improves the workflow readability by replacing variables,
simplifying if() clauses and orderings etc.

Resolves: #83922
Releases: master
Change-Id: I893ad348f8976dd65bf11a117f54433b46d0d896
Reviewed-on: https://review.typo3.org/55738


Reviewed-by: Mathias Schreiber <mathias.schreiber@typo3.com>
Tested-by: Mathias Schreiber <mathias.schreiber@typo3.com>
Reviewed-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Tested-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Susanne Moog <susanne.moog@typo3.org>
Tested-by: Susanne Moog <susanne.moog@typo3.org>