[BUGFIX] EXT:form - Fix broken inArray validator

Handle different configuration types and multiselect values.

Resolves: #75576
Releases: master, 7.6
Change-Id: I42c0bcbc5f5307d125484149108495ea971a692e
Reviewed-on: https://review.typo3.org/47661


Reviewed-by: Bjoern Jacob <bjoern.jacob@tritum.de>
Tested-by: Bjoern Jacob <bjoern.jacob@tritum.de>
Reviewed-by: Daniel Lorenz <info@extco.de>
Tested-by: Daniel Lorenz <info@extco.de>
Reviewed-by: Daniel Goerz <ervaude@gmail.com>
Reviewed-by: Morton Jonuschat <m.jonuschat@mojocode.de>
Tested-by: Morton Jonuschat <m.jonuschat@mojocode.de>