[TASK] Handle JSON problems in RedisSessionBackend

We now make sure that JSON en- and decoding works flawlessly,
otherwise we throw the usual exceptions instead of failing
with PHP errors.

Resolves: #90744
Releases: master, 9.5
Change-Id: I7f791a73906447f0879590bee6f51143b7089ba5
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/63713


Tested-by: TYPO3com <noreply@typo3.com>
Tested-by: Susanne Moog <look@susi.dev>
Tested-by: Benni Mack <benni@typo3.org>
Reviewed-by: Georg Ringer <georg.ringer@gmail.com>
Reviewed-by: Susanne Moog <look@susi.dev>
Reviewed-by: Benni Mack <benni@typo3.org>