iOS: Make window-scrolling optional for Items

On iOS Qt scrolls the rootview up, when a text input gets focus (in qtbase\src\plugins\platforms\ios\qiosinputcontext.mm). 

While this is certainly useful in many occasions, in other occasions it is a huge pain in the behind.

Right now I'm trying to implement a text editor with a toolbar anchored to the keyboard and a header (which should stay at the top). It seems to be almost impossible (at least after about 7-8 hours trying).

I suggest making this scrolling optional for individual items (via attached property) or toggleable via a function call ( Qt.setAutoScrollEnabled(bool) ).