[TASK] Rename $sortRow to $sortColumn in DataHandler

The new name makes the code easier to understand, as the variable
contains the column name configured in ['ctrl']['sortby'].

Resolves: #85258
Releases: master
Change-Id: I0237809c9029a634a50753a6978f74831ae8c14f
Reviewed-on: https://review.typo3.org/57214


Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Markus Klein <markus.klein@typo3.org>
Tested-by: Markus Klein <markus.klein@typo3.org>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>