[!!!][TASK] Remove AbstractUserAuthentication->svConfig

The public property svConfig is just a short-hand variable
for $GLOBALS['TYPO3_CONF_VARS']['SVCONF']['auth'],
but should not be accessed from the outside, and is therefore
moved from a public property to a local variable within the
"checkAuthentication" method where it is mainly used.

Resolves: #92990
Releases: master
Change-Id: I1f8cadc36b22e535efb1940c8090ff5e487952bb
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/67002


Tested-by: TYPO3com <noreply@typo3.com>
Tested-by: Oliver Bartsch <bo@cedev.de>
Tested-by: Andreas Fernandez <a.fernandez@scripting-base.de>
Reviewed-by: Oliver Bartsch <bo@cedev.de>
Reviewed-by: Andreas Fernandez <a.fernandez@scripting-base.de>