[TASK] Deprecate extbase feature toggles

Extbase has an own feature toggle system. This
is based on TypoScript configuration and the
awful ConfigurationManager.

TYPO3 v10 introduces a core-based feature toggle
system based on TYPO3_CONF_VARS, so extbase
overlaps here, and we should get rid of it.

Current extbase uses feature toggles for two
ancient details, and one option that has been
added with TYPO3 v12.

The patch deprecates the PHP API and all toggles.

In case extbase implements functionality again
that needs to be toggled, it should be based
on the core feature toggle API instead. Doing
this per-extension can be done by prefixing
them accordingly if needed.

Resolves: #100622
Related: #97096
Releases: main
Change-Id: I5776c57af85aa01c97bc0d7fe7eeaf148a3e5016
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/78670


Tested-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Reviewed-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Tested-by: Stefan Bürk <stefan@buerk.tech>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: core-ci <typo3@b13.com>
Reviewed-by: Stefan Bürk <stefan@buerk.tech>