The patch deprecates BackendUserAuthentication->getTSConfigVal()
and ->getTSConfigProp() and adapts usages to rely on getTSConfig()
without arguments. The array nesting is done directly within
consuming code and is combined with ?? to a fallback value.
Advantages:
* Expensive and recursive string operations within
  getTSConfig() are not used anymore.
* The weird 'value' / 'property' based sub array
  juggling is gone.
* Full TSconfig path including fallback can be easily
  seen within consuming code
* Notice free array access using null coalescence operator

Change-Id: I6d5777ebd533dcfdc6018e0226bfb3e513cfa652
Resolves: #84993
Related: #84982
Releases: master
Reviewed-on: https://review.typo3.org/56953


Reviewed-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Tested-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Reviewed-by: Stefan Neufeind <typo3.neufeind@speedpartner.de>
Tested-by: Stefan Neufeind <typo3.neufeind@speedpartner.de>
Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Tested-by: Wouter Wolters <typo3@wouterwolters.nl>