Fix style animations to stop when the item is hidden

Fix style animations to stop when the item is hidden

QStyleAnimation automatically stopped for hidden QWidgets, but didn't
know anything about QQuickItems and kept animating regardless of their
visibility. QStyleAnimation was changed so that it will keep animating
only as long as the animation target accepts animation updates. This
change ensures that the style animation updates are accepted only when
the item is visible.

Task-number: QTBUG-35319
Change-Id: I3c93a653316b8abbbc32940cd7499b660828eff8
Reviewed-by: Gunnar Sletta <gunnar.sletta@digia.com>
Reviewed-by: Jens Bache-Wiig <jens.bache-wiig@digia.com>