[BUGFIX] Correctly handle identical arrays in arrayDiffAssocRecursive

Add a new test to make sure that identical input arrays also deliver
an empty result as difference.

Resolves: #84067
Releases: master, 8.7, 7.6
Change-Id: Ia16ca9560094c4ae42eb69cac9e09cd4bef7dc4e
Reviewed-on: https://review.typo3.org/55925


Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Markus Klein <markus.klein@typo3.org>
Tested-by: Markus Klein <markus.klein@typo3.org>