FileReferences objects contain references to File
objects which itself contain service dependencies
(e.g. event dispatcher) which are not seralizable.

This leads to problems for instance when having
a multi-step form containing file uploads where
file reference objects are being serialized.

Resolves: #91196
Releases: master, 10.4
Change-Id: I7650186adc5c61528e1a1adcf06b8d6cf67a55cd
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/64841Tested-by: TYPO3com <noreply@typo3.com>
Tested-by: Oliver Hader <oliver.hader@typo3.org>
Tested-by: Daniel Goerz <daniel.goerz@posteo.de>
Reviewed-by: Oliver Hader <oliver.hader@typo3.org>
Reviewed-by: Daniel Goerz <daniel.goerz@posteo.de>