[BUGFIX] EXT:form - respect class for file upload field

Resolves: #83260
Releases: master, 8.7
Change-Id: I04c0bfa08ceb19ed0f797107ac307b06a77b4dcb
Reviewed-on: https://review.typo3.org/54991


Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Bjoern Jacob <bjoern.jacob@tritum.de>
Tested-by: Bjoern Jacob <bjoern.jacob@tritum.de>
Reviewed-by: Susanne Moog <susanne.moog@typo3.org>
Tested-by: Susanne Moog <susanne.moog@typo3.org>