[BUGFIX] EXT:form - merge properties with configuration settings

Merge the properties set through the formDefinition with the
predefined properties from the base configuration.
Add tests for property part of FormElementInterface implementation.

Resolves: #82243
Releases: master, 8.7
Change-Id: Ia6a4428aa52508ec6756eaa6a9d9c471e932baf8
Reviewed-on: https://review.typo3.org/54124


Reviewed-by: Daniel Lorenz <daniel.lorenz@extco.de>
Tested-by: Daniel Lorenz <daniel.lorenz@extco.de>
Reviewed-by: Carlos Meyer <cm@davitec.de>
Tested-by: Carlos Meyer <cm@davitec.de>
Reviewed-by: Stefan Neufeind <typo3.neufeind@speedpartner.de>
Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Susanne Moog <susanne.moog@typo3.org>
Tested-by: Susanne Moog <susanne.moog@typo3.org>