[BUGFIX] Fix position of buttons in RTE full screen mode

Update the HTML markup for the action buttons in the RTE full screen
view to properly position the buttons there.

Releases: 6.3, 6.2
Resolves: #60119
Change-Id: I0c06dd5fa5a7975a3ddcddb58c3b44d41da2192a
Reviewed-on: https://review.typo3.org/31474
Reviewed-by: Marcin Sągol
Tested-by: Marcin Sągol
Reviewed-by: Wouter Wolters
Tested-by: Wouter Wolters