[BUGFIX] Respect non standard prototype names

The patchset https://review.typo3.org/c/Packages/TYPO3.CMS/+/70460/
has moved the business logic from the RenderViewHelper to the
FormRequestHandler.
Thereby the process for detecting the prototype name was changed by
mistake.
The result is that custom prototype names are no longer applied.
This patchset restores the correct behavior.

Resolves: #98023
Releases: main, 11.5
Change-Id: I5d59e56c0c071879ad60321dd9d82a56cde94172
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/75225


Tested-by: Daniel Gohlke <daniel.gohlke@extco.de>
Tested-by: core-ci <typo3@b13.com>
Tested-by: Björn Jacob <bjoern.jacob@tritum.de>
Tested-by: waldhacker <hello@waldhacker.dev>
Reviewed-by: Daniel Gohlke <daniel.gohlke@extco.de>
Reviewed-by: Björn Jacob <bjoern.jacob@tritum.de>
Reviewed-by: waldhacker <hello@waldhacker.dev>