Move QShortcutMap to QtGui.

After the move of QWidgets in their own library there is no way to have shortcuts working inside QtGui. We can't add action on a QWindow and even if we use the old QMainWindow, the shortcuts are not properly triggered if a QWindow is active as the events are directly delivered to the window rather than using QApplication::notify. Supporting that would require to move the QShortcutMap back to QtGui.