[!!!][TASK] Declare all ViewHelpers final

As anticipated in v11 with #95298, this patch
declares ViewHelper classes PHP final, third party
extensions can no longer extend core ViewHelpers.

There is one exception: The ext:fluid FormViewHelper,
which is currently extended by ext:form. This can't
be resolved easily since it's on one hand quite a bit
of code that would have to be copied, and more importantly,
the FormField* ViewHelpers refer to the "parent"
FormViewHelper class name in various places. Declaring
FormViewHelper final thus needs a different refactoring,
which may be done in v12 with further patches.

Resolves: #96368
Related: #95298
Releases: main
Change-Id: I7e8a587dadef4e411390710dd47e309cd2414e65
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/72671


Tested-by: core-ci <typo3@b13.com>
Tested-by: Stefan Bürk <stefan@buerk.tech>
Tested-by: Benni Mack <benni@typo3.org>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Stefan Bürk <stefan@buerk.tech>
Reviewed-by: Oliver Bartsch <bo@cedev.de>
Reviewed-by: Benni Mack <benni@typo3.org>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>