[BUGFIX] Cover multi-value properties in form editor with HMAC

With #85044, HMAC validation for form definitions in the backend form
editor was introduced. However, nested multi-valued options have not
been signed with corresponding HMAC values - which lead to error
messages when persisting the form again in the backend.

The exception for `_value` and `_label` (properties used for those
multi-valued items) have been removed when generating HMAC values.

Resolves: #94106
Resolves: #97235
Related: #85044
Releases: main, 11.5, 10.4
Change-Id: Iaf6798e0f5aa43bdaf90b2c1866745abaab25de1
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/76165


Tested-by: core-ci <typo3@b13.com>
Tested-by: Oliver Hader <oliver.hader@typo3.org>
Reviewed-by: Oliver Hader <oliver.hader@typo3.org>