[TASK] Simplify DH by inlining SlugEnricher

DataHandler related class SlugEnricher is a scary
sounding class name for a simple operation that
sets incoming TCA type=slug fields to empty string
if not provided, to trigger slug calculation later.

The patch inlines that operation into DataHandler,
avoiding the class with three methods, a property,
and a set of array_* function calls, substituting
it with three foreach(), two if() and a helper
method that can be re-used.

Change-Id: I4452d9c50b43832db3cd4b7f538395054a3d67ab
Resolves: #103244
Releases: main
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/83176


Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Tested-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
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>