[FEATURE] Add identifier to callback of Wizard.addSlide()

The callback of ``Wizard.addSlide()`` has now a third parameter
``identifier`` holding the identifier of the current slide.

Resolves: #75386
Releases: master
Change-Id: I34dd9f176782fe88a8aaf8d6af09d019261803a9
Reviewed-on: https://review.typo3.org/47501


Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Tested-by: Wouter Wolters <typo3@wouterwolters.nl>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>