[BUGFIX] Add fallback identifier to IRRE fields

In case of IRRE in site context not the full form engine variables
are available - therefor a fallback has been implemented.

Resolves: #89628
Releases: master, 9.5
Change-Id: I0c499d41354e4dc369f5a53f2109d8559b5e3bcb
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/62265


Tested-by: Daniel Goerz <daniel.goerz@posteo.de>
Tested-by: TYPO3com <noreply@typo3.com>
Tested-by: Oliver Bartsch <bo@cedev.de>
Tested-by: Benni Mack <benni@typo3.org>
Reviewed-by: Daniel Goerz <daniel.goerz@posteo.de>
Reviewed-by: Oliver Bartsch <bo@cedev.de>
Reviewed-by: Benni Mack <benni@typo3.org>