[TASK] Deprecate fluid HtmlViewHelper in Backend context

The HtmlViewHelper relies of Frontend TypoScript
"parseFunc" functionality and has an ugly hack
to prepare Frontend rendering in Backend context.

The core no longer uses f:format.html in Backend
context since the introduction of f:sanitize.html
and f:transform.html. Using f:format.html in
Backend context should be deprecated.

Resolves: #99031
Related: #94825
Releases: main
Change-Id: I60c5ea36b664a35abde431d2ac845ee9e2bff4bb
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/76519


Tested-by: core-ci <typo3@b13.com>
Tested-by: Oliver Hader <oliver.hader@typo3.org>
Tested-by: Oliver Bartsch <bo@cedev.de>
Tested-by: Susanne Moog <look@susi.dev>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Oliver Hader <oliver.hader@typo3.org>
Reviewed-by: Oliver Bartsch <bo@cedev.de>
Reviewed-by: Susanne Moog <look@susi.dev>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>