The old class name is still in use in the core, replace them
with the new name DataHandler.

Resolves: #78550
Releases: master
Change-Id: I324e7b3037f8bf8df70d5c8db37d62a01ed710a4
Reviewed-on: https://review.typo3.org/50485


Reviewed-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Tested-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Tymoteusz Motylewski <t.motylewski@gmail.com>
Tested-by: Tymoteusz Motylewski <t.motylewski@gmail.com>