QQuickItemLayer now has a live property that can be set to determine if
its contents should change whenever the item updates. This enables
variable refresh rate for quick items.
[ChangeLog] Added live property to QQuickItem layer.
Fixes: QTBUG-77343
Change-Id: I8bf7e7af4cfed6deef2253d346bb0b72d0fef66e
Reviewed-by: Laszlo Agocs <laszlo.agocs@qt.io>