[BUGFIX] Use correct FlexForm field names in debug info

The debug information of each element
in FormEngine now displays the correct
field names for FlexForm fields in a
container. Additionally, do the container
elements itself display the correct
(field) name now.

Resolves: #104303
Releases: main, 12.4
Change-Id: Ic2a92bc0deea4b3165f4aa77103c56050cb3dc63
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/85096


Tested-by: Garvin Hicking <gh@faktor-e.de>
Reviewed-by: Garvin Hicking <gh@faktor-e.de>
Tested-by: Georg Ringer <georg.ringer@gmail.com>
Tested-by: core-ci <typo3@b13.com>
Reviewed-by: Georg Ringer <georg.ringer@gmail.com>
Reviewed-by: Oliver Bartsch <bo@cedev.de>
Tested-by: Oliver Bartsch <bo@cedev.de>