[BUGFIX] Add missing identify fields for f:hidden VH

When using only f:hidden fields for sub-properties
of a domain model which has to be updated, no identity
fields (__identity) are generated in HTML which
results in creating new model instead of updating it.

Resolves: #90331
Releases: master, 9.5
Change-Id: Ic14478a682a98bb96c27567da23b69da359cb726
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/63177


Reviewed-by: Daniel Goerz <daniel.goerz@posteo.de>
Reviewed-by: Oliver Bartsch <bo@cedev.de>
Reviewed-by: Georg Ringer <georg.ringer@gmail.com>
Reviewed-by: Susanne Moog <look@susi.dev>
Tested-by: TYPO3com <noreply@typo3.com>
Tested-by: Georg Ringer <georg.ringer@gmail.com>
Tested-by: Susanne Moog <look@susi.dev>