allow lti content to enter full screen mode

Test Plan
- lti content should be able to enter full screen mode

fixes PLAT-614

Change-Id: Icffa991ca618cc6aeab2ac5ba0743746ab8bac41
Reviewed-on: https://gerrit.instructure.com/40320
Reviewed-by: Bracken Mosbacker <bracken@instructure.com>
Product-Review: Bracken Mosbacker <bracken@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>
QA-Review: Clare Strong <clare@instructure.com>