[TASK] Clean up ErrorHandler

The error handler now uses LogLevel
constants in various places, except for sys_log
where the severity is manually resolved.

Resolves: #94783
Releases: master
Change-Id: I6e7fd00510e59c0bc3c661bb21dd42453a5c835e
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/70285


Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Reviewed-by: crell <larry@garfieldtech.com>
Reviewed-by: Rudy Gnodde <rudy@famouswolf.com>
Reviewed-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: core-ci <typo3@b13.com>
Tested-by: Wouter Wolters <typo3@wouterwolters.nl>
Tested-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>