Mouse co-ordinates are not always adjusted when MouseArea's state changes

This was seen with QML compiled from qt/qt-qml and HEAD at
5eb8e749bdd60ce93737b96f8f736796dfa77281 and tesla with HEAD at
a1ac83bfa94cb23f9e7518c3d82def89555e91b1

Clicking within a MouseArea without moving the mouse now generates the
following events
1) onPressed
2) onPositionChanged
3) onReleased
4) onClicked

If at any point the MouseArea's state (e.g, size and position) change, this must
be reflected in the mouse coordinates reported to each subsequent event.
Currently this is not the case.

In the case of tesla, the implementation of the onPressed signal reparents the
MouseArea and makes it full screen, yet the mouseX and mouseY reported to
the onPositionChanted event that follows does not adjust the coordinates for
this.

To see the problem, launch tesla and open the launcher page and scroll to the
second page. Then long-press an icon to enter edit mode, then tap any icon
and note how the it disappears. It has in face been moved to the previous page
(once the page is full the icons stay then tapped). Note that dragging the mouse
even slightly before releasing the button avoids this problem.