[BUGFIX] Fix blacklist in DebuggerUtility::var_dump

Wrong usage of strpos leads to not respecting the given blacklist.
Use in_array instead to solve the problem.

Resolves: #72407
Releases: master,7.6
Change-Id: I774bb7c4c9c2bd1c32b2955368b5d9033256100b
Reviewed-on: https://review.typo3.org/49229


Tested-by: Bamboo TYPO3com <info@typo3.com>
Reviewed-by: Susanne Moog <susanne.moog@typo3.org>
Tested-by: Susanne Moog <susanne.moog@typo3.org>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>