[TASK] Add cache to IconUtility::getSpriteIcon()

Cache calls to getSpriteIcon() that only use the first parameter.

Change-Id: I63e7dbaf81473b733a73f4a964e419dae0650f5f
Resolves: #56110
Releases: 6.2
Reviewed-on: https://review.typo3.org/27713
Reviewed-by: Wouter Wolters
Tested-by: Wouter Wolters