[TASK] Use double back slashes for class name in makeInstance

Resolves: #60562
Releases: 6.3
Change-Id: I321f32f85df90e11443837c2704eba5c097e7ea1
Reviewed-on: http://review.typo3.org/31808
Reviewed-by: Susanne Moog <typo3@susannemoog.de>
Tested-by: Susanne Moog <typo3@susannemoog.de>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Tested-by: Anja Leichsenring <aleichsenring@ab-softlab.de>