QWheelEvent high-resolution delta support.

QWheelEvent high-resolution delta support.

Support pixel-based deltas as well as sending
dx and dy values in the same event. Keep source and
behavior compatibility with Qt 4.

New API:
QPoint pixelDelta() const
QPoint angleDelta() const

Deprecate delta() and orientation().

Both pixel-based deltas and combined updates are
necessary for smooth trackpad-based scrolling on
OS X.

Qt 4 compatible behavior is achieved by sending an
extra wheel event in cases where the initial event
has a combined dx and dy update. This extra event
sends dx in delta() and orientation(), with pixelDelta()
and angleDelta() set to null.

Modify the Cocoa implementation to provide pixel
deltas. It is expected that not all platforms can
provide these. Angle deltas will always be available.

Change-Id: I20c10f0df338ddcd6a3f7a4d40949ed5ae3b4795
Reviewed-by: Morten Johan Sørvig <morten.sorvig@nokia.com>