Enable mouse tracking on construction of every wxQt widget

Not all controls use wxWindow::Create(), so move setMouseTracking() call
where it is always executed.

Closes https://github.com/wxWidgets/wxWidgets/pull/1528

include/wx/qt/private/winevent.h

@@ -61,6 +61,7 @@ public:
         QObject::connect( this, &QObject::destroyed, this,
                           &wxQtEventSignalHandler::HandleDestroyedSignal );
 
+        Widget::setMouseTracking(true);
     }
 
     void HandleDestroyedSignal()