QML Flickable truncates contentX to signed 32-bits (0x80000000)

QML Flickable will truncate contentX to 0x80000000 on mouse release or when animated movement crosses the 32-bit signed boundary of 0x7fffffff..0x80000000

To reproduce:

• load attached main.qml
• mouse drag the blue rectangle to see the contentX changing around zero
• click the orange button to set contentX to 0x80000000
• mouse drag and see int64 large numbers are supported (contentX > 0x80000000)
• release mouse with contentX > 0x80000000, contentX snaps back to 0x80000000
• setup movement with contentX < 0x80000000, contentX snap halts at 0x80000000