[TASK] EXT:form - license headers

Add a reference to the original authors since most of the
Frontend functionality is heavily inspired and copied from
the Neos/Flow Form package.

Resolves: #79074
Releases: master
Change-Id: I178a7314a0da70a7406df3bcc58f3dd28bdff463
Reviewed-on: https://review.typo3.org/51025


Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Tested-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Reviewed-by: Georg Ringer <georg.ringer@gmail.com>
Tested-by: Georg Ringer <georg.ringer@gmail.com>