Fix mouse handling in qml-compositor.

The pointer focus must be set in pressed. We cannot rely on
the implicit mouse tracking behavior of QWindow for QML stuff
because the WaylandSurfaceItems will not get mouse moves outside
of a press-release sequence.

Change-Id: Ic2cf2a7497cac7397bcfa26440dd05cded6182dc
Sanity-Review: Qt Sanity Bot <qt_sanity_bot@ovi.com>
Reviewed-by: Jørgen Lind <jorgen.lind@nokia.com>

src/compositor/compositor_api/waylandsurfaceitem.cpp

@@ -149,6 +149,8 @@ void WaylandSurfaceItem::mousePressEvent(QMouseEvent *event)
 {
     if (m_surface) {
         WaylandInputDevice *inputDevice = m_surface->compositor()->defaultInputDevice();
+        if (inputDevice->mouseFocus() != m_surface)
+            inputDevice->setMouseFocus(m_surface, event->pos(), event->globalPos());
         inputDevice->sendMousePressEvent(event->button(), toSurface(event->pos()));
     }
 }