[TASK] Avoid a pass-by-reference in DataHandler

There is no point calling addDefaultPermittedLanguageIfNotSet()
with $incomingFieldArray as reference. It is more easy to see
the method can change $incomingFieldArray when it simply
returns the updated array instead.

Resolves: #102173
Releases: main
Change-Id: If048cc438e53afca7a207200190689074963d2e2
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/81431


Reviewed-by: Oliver Klee <typo3-coding@oliverklee.de>
Reviewed-by: Jasmina Ließmann <minapokhalo+typo3@gmail.com>
Reviewed-by: Stefan Bürk <stefan@buerk.tech>
Tested-by: core-ci <typo3@b13.com>
Tested-by: Oliver Klee <typo3-coding@oliverklee.de>
Tested-by: Stefan Bürk <stefan@buerk.tech>