[BUGFIX] Correct type for constants linkWrap height and width

The height and width have a default value with a "m" in it.
This is stripped of because the wrong data type is used. Use string
instead to circumvent the automatic stripping of the letter "m".

Resolves: #75520
Releases: master,7.6
Change-Id: I36c18e955db50ecd981efd24a0f842706d8d0fdc
Reviewed-on: https://review.typo3.org/48375


Reviewed-by: Oliver Hader <oliver.hader@typo3.org>
Tested-by: Oliver Hader <oliver.hader@typo3.org>
Reviewed-by: Michael Oehlhof <typo3@oehlhof.de>
Reviewed-by: Markus Klein <markus.klein@typo3.org>
Tested-by: Markus Klein <markus.klein@typo3.org>