[TASK] Protect user TSconfig properties in BackendUserAuthentication

The patch sets all user TSconfig related properties of class
BackendUserAuthentication to protected. Existing usages of
property "userTS" are adapted to call getTSConfig() instead.

Resolves: #84984
Related: #84982
Releases: master
Change-Id: I6fd10164c29959e4e705699776d694d63d7f5596
Reviewed-on: https://review.typo3.org/56940


Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Tested-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Reviewed-by: Andreas Wolf <andreas.wolf@typo3.org>
Tested-by: Andreas Wolf <andreas.wolf@typo3.org>