iOS: calculate bounds in desktop view using transformed window bounds for both width...

iOS: calculate bounds in desktop view using transformed window bounds for both width and height

Depending on the orientation, UIKit might shrink either the width or the height
of the view to fit the status bar. Since we anyway want the view to fill the whole
window, we simply ignore this, and use the bounds of the whole window directly.

Task-number: QTBUG-47506
Change-Id: I73294e5792f8d98fb0c0b0a42198207baca08e3c
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@theqtcompany.com>