[BUGFIX] Get the correct crop configuration for imgResource

This fix returns the right ImageManipulation\Area object
in case the imgResource "crop" value is a json string with variants.

Resolves: #82057
Releases: master, 8.7
Change-Id: Ibfc9f33ffc060992f22c1a3c7326990834f02ec4
Reviewed-on: https://review.typo3.org/53717


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: Benni Mack <benni@typo3.org>
Tested-by: Benni Mack <benni@typo3.org>