[TASK] Improve type annotations for ImageDimension

Resolves: #101989
Releases: main
Change-Id: Ifb2a68271f8e9dcd0bf37834fc673587a3cbcfcd
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/81129


Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: core-ci <typo3@b13.com>
Tested-by: Benni Mack <benni@typo3.org>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Benni Mack <benni@typo3.org>