[TASK] Prepare stateless DiffUtility

DiffUtility has the unfortunate property
`$stripTags`, making this tiny service
stateful. This service should not
`strip_tags()` on its own, consumers should,
if needed.

The patch adds a new method `diff()`, that
does not strip tags anymore and deprecates
the property and method `makeDiffDisplay()`.

Resolves: #104325
Releases: main
Change-Id: Ib6705816bf1547bc2a54eb5bb364fdcde4c10ea9
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/85141


Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: core-ci <typo3@b13.com>
Tested-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Reviewed-by: Benni Mack <benni@typo3.org>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Tested-by: Benni Mack <benni@typo3.org>