[BUGFIX] Flatten nesting of formengine-field-item in web components

Resolves: #100540
Releases: main
Change-Id: I4acdefdf455bff6e855ce130c8165a398f271a6f
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/78548


Tested-by: core-ci <typo3@b13.com>
Tested-by: Frank Nägler <frank.naegler@typo3.com>
Tested-by: Andreas Fernandez <a.fernandez@scripting-base.de>
Reviewed-by: Andreas Fernandez <a.fernandez@scripting-base.de>
Reviewed-by: Frank Nägler <frank.naegler@typo3.com>