[FEATURE] Migrate icon sizes to enum

The icon size constants defined in `\TYPO3\CMS\Core\Imaging\Icon` are
moved into a new `TYPO3\CMS\Core\Imaging\IconSize` enum. All method
accepting the old string constants are adapted to accept the enum class
as well, while triggering a deprecation when a string is passed for
compatibility reasons.

Resolves: #101475
Releases: main
Change-Id: Idd61594ed21b30033d13b4c653992756e66db7c1
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/80197


Tested-by: Andreas Fernandez <a.fernandez@scripting-base.de>
Reviewed-by: Stefan B�rk <stefan@buerk.tech>
Tested-by: Stefan B�rk <stefan@buerk.tech>
Tested-by: core-ci <typo3@b13.com>
Reviewed-by: Andreas Fernandez <a.fernandez@scripting-base.de>
Tested-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Reviewed-by: Anja Leichsenring <aleichsenring@ab-softlab.de>