Change Screen Split Icon in Topbar to Rotate Screen

[robin]

this is just a wish. I do not know how many people are often using split screen, but I wouldn't think that those are majority as the screenscrolling of shr-u is now very fast and we don't have too many application = icons anyway.
Therefore I suggest to change this button to a rotate screen button, as this would be very helpful when writing sms for example.