[TASK] Convert IconFactoryTest to functional test

This reduces the amount of mocking drastically.

Resolves: #96758
Releases: main, 11.5
Change-Id: Ia6d5e6086c23de4fe8c4ff8f95b20cc5320ae837
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/73316


Tested-by: core-ci <typo3@b13.com>
Tested-by: Oliver Klee <typo3-coding@oliverklee.de>
Tested-by: Stefan Bürk <stefan@buerk.tech>
Tested-by: Georg Ringer <georg.ringer@gmail.com>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Oliver Klee <typo3-coding@oliverklee.de>
Reviewed-by: Stefan Bürk <stefan@buerk.tech>
Reviewed-by: Georg Ringer <georg.ringer@gmail.com>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>