[TASK] Make IGNORED_EXCEPTION_CODES accessible

This makes AbstractExceptionHandler::IGNORED_EXCEPTION_CODES public accessible in order to re-use it in custom error handlers.

Resolves: #100720
Releases: main, 11.5
Change-Id: Id9217d3bbf3b66982adceb485918e52bb5cddd56
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/78735


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