[BUGFIX] Mark erroneous fields within `.formengine-field-item`

FormEngine UI has a rather inconsistent markup. Fields within
Flexforms may appear within another `div` container, causing issues
when trying to mark an erroneous field as such. To solve this
short-termed, additional CSS rules are added to cover such cases.

In the long run, the FormEngine markup must get consolidated.

Resolves: #102252
Releases: main, 12.4
Change-Id: I671fd8fe2edbd2b3592e7f4e1f205544a074ec51
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/81557


Tested-by: core-ci <typo3@b13.com>
Tested-by: Jasmina Ließmann <minapokhalo+typo3@gmail.com>
Reviewed-by: Jasmina Ließmann <minapokhalo+typo3@gmail.com>