[TASK] EXT:form - Rename "Vendor" javascript folder to "Contrib"

Move folder typo3/sysext/form/Resources/Public/JavaScript/Backend/Vendor
to typo3/sysext/form/Resources/Public/JavaScript/Contrib.

Resolves: #83879
Releases: master, 8.7
Change-Id: I35cefa13bcfa621d4877273267d58ff4e26cd5bd
Reviewed-on: https://review.typo3.org/55815


Reviewed-by: Björn Jacob <bjoern.jacob@tritum.de>
Tested-by: Björn Jacob <bjoern.jacob@tritum.de>
Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Frank Naegler <frank.naegler@typo3.org>
Tested-by: Frank Naegler <frank.naegler@typo3.org>