[TASK] Properly double-backslash some backslashes in strings

Resolves: #47198
Releases: 6.2
Change-Id: I56c1221b58ce08868ff755c4a54b0fa9f4447aff
Reviewed-on: https://review.typo3.org/19948
Reviewed-by: Wouter Wolters
Tested-by: Wouter Wolters