[TASK] EXT:form - fix documentation paths

Cleanup some leftovers from issue #82336 (review:53946) within
the EXT:form documentation. Basically, long file paths are shortened.

Resolves: #82472
Related: #82336
Releases: master
Change-Id: I6ecac403a91d195d0c35d99281ecbe665ca8ec54
Reviewed-on: https://review.typo3.org/54132


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