[SECURITY] Ensure text preview of multivalue items in form editor

Multivalue items in the form editor user interface were previewed
as HTML, but should be treated as scalar text only.

Resolves: #96743
Releases: main, 11.5, 10.4
Change-Id: I5e8dab26119490ecf19ac5d48c2bc7a5a00daaad
Security-Bulletin: TYPO3-CORE-SA-2022-003
Security-References: CVE-2022-31048
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/74894


Tested-by: Oliver Hader <oliver.hader@typo3.org>
Reviewed-by: Oliver Hader <oliver.hader@typo3.org>