[BUGFIX] EXT:form - use configured finisher identifiers for translations

Use the configured finisher identifier for translation keys instead of
the finisher class name.

Resolves: #81591
Releases: master, 8.7
Change-Id: Ib78e942121b4b6e299ae394c30261603760444f7
Reviewed-on: https://review.typo3.org/53363


Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Denis Mir <mir.denis@googlemail.com>
Tested-by: Denis Mir <mir.denis@googlemail.com>
Reviewed-by: Bjoern Jacob <bjoern.jacob@tritum.de>
Tested-by: Bjoern Jacob <bjoern.jacob@tritum.de>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>