[BUGFIX] Properly append/prepend with "addRecord" wizard

For relations the internal field value contains a list of UIDs instead
of full related records.

Resolves: #82461
Releases: master, 8.7
Change-Id: Iec2a74fbc8d17636dd8751911984c337d4e99b63
Reviewed-on: https://review.typo3.org/55826


Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Tobi Kretschmann <tobi@tobishome.de>
Reviewed-by: Markus Klein <markus.klein@typo3.org>
Reviewed-by: Kevin Ditscheid <kevinditscheid@gmail.com>
Tested-by: Kevin Ditscheid <kevinditscheid@gmail.com>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>