[BUGFIX] Proper styleguide data generator MM fields

Patch for #102279 to auto-create DB select fields
reveals a bug in the styleguide data generator which
tries to create (partially empty) strings for the
"parent count" fields when select is configured with
MM.
The patch adapts the generator logic a bit to create
better values in those cases.

Resolves: #102704
Related: #102279
Releases: main
Change-Id: I236e1c6d5c1ce8abfa1e84fc35b6aa6c2765d762
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/82263


Tested-by: core-ci <typo3@b13.com>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Tested-by: Stefan Bürk <stefan@buerk.tech>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Reviewed-by: Stefan Bürk <stefan@buerk.tech>