[TASK] Deprecate BackendUtility::thumbCode()

The method is unused in core and also is considered
bad API, e.g. because of a couple of method arguments
are unused, while other have been added over time
to change behaviour.

Resolves: #104662
Releases: main
Change-Id: Ibe9057dcd7d86995c8bb664cb47be4f3ea043b03
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/85680


Reviewed-by: Oliver Bartsch <bo@cedev.de>
Reviewed-by: Stefan Bürk <stefan@buerk.tech>
Reviewed-by: Andreas Nedbal <andy@pixelde.su>
Tested-by: Oliver Bartsch <bo@cedev.de>
Tested-by: Jochen Roth <rothjochen@gmail.com>
Tested-by: Stefan Bürk <stefan@buerk.tech>
Tested-by: core-ci <typo3@b13.com>
Reviewed-by: Garvin Hicking <gh@faktor-e.de>
Reviewed-by: Jochen Roth <rothjochen@gmail.com>
Tested-by: Andreas Nedbal <andy@pixelde.su>
Tested-by: Garvin Hicking <gh@faktor-e.de>