[SECURITY] Protect core Ajax calls against CSRF

The backend ajax handler that are directly registered
in DefaultConfiguration.php are now CSRF protected
if necessary.

Resolves: #56356
Releases: 6.2
Change-Id: Ia592f7f2b51c20326600b97d2ce10a5e5fdbfde7
Reviewed-on: https://review.typo3.org/27877
Reviewed-by: Wouter Wolters
Tested-by: Wouter Wolters
Reviewed-by: Markus Klein
Tested-by: Markus Klein