[ios] Onscrolled returns X offset instead of scroll Y delta

[ilyaqznetsow]

Ios renderers OnScroll event returns 0 as a Delta value when using fastgrid as vertical collection view.

void HandleOnScrolled(CGPoint contentOffset, ScrollActionType type) { if (Element == null) return; Element.RaiseOnScroll(contentOffset.X, contentOffset.X, contentOffset.Y, type); The first arguement of RaiseOnScroll should be something like contentOffset.Y - _oldOffset