[BUGFIX] Correct horizontal scrolling in iframe on iOS browsers

Browsers on iOS are ignoring the width property for iframes,
this resulted in iframes beeing rendered too wide and prevented
scrolling on the horizontal axis.

Resolves: #83841
Releases: master, 8.7
Change-Id: I825d6f911959fdb588f1f164f0ec4bbbf5c067c0
Reviewed-on: https://review.typo3.org/55649


Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Mathias Schreiber <mathias.schreiber@typo3.com>
Tested-by: Mathias Schreiber <mathias.schreiber@typo3.com>
Reviewed-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Tested-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Reviewed-by: Benjamin Kott <benjamin.kott@outlook.com>
Tested-by: Benjamin Kott <benjamin.kott@outlook.com>