[TASK] Streamline GlobalEventHandler JavaScript module

* streamline variable names
* streamline method names
* preparation for additions in the future

Resolves: #91805
Releases: master, 10.4
Change-Id: Iaa16cfcbcda7adbd48838a498f2f459d97f4ef18
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/65042


Tested-by: TYPO3com <noreply@typo3.com>
Tested-by: Oliver Hader <oliver.hader@typo3.org>
Reviewed-by: Oliver Hader <oliver.hader@typo3.org>