[TASK] Use JsonResponse for all Backend AJAX calls

The new JsonResponse object should be used throughout the
TYPO3 Backend in order to properly call json_encode() with
the right flags automatically, making the code inside
the controllers simpler.

Resolves: #83267
Releases: master
Change-Id: Ie03fb1414a965a61632897f0e25645a67f3225a5
Reviewed-on: https://review.typo3.org/54995


Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Stefan Neufeind <typo3.neufeind@speedpartner.de>
Tested-by: Stefan Neufeind <typo3.neufeind@speedpartner.de>
Reviewed-by: Susanne Moog <susanne.moog@typo3.org>
Tested-by: Susanne Moog <susanne.moog@typo3.org>