Support AutoScroll while mouse tracking is enabled

AutoScrollHandler generates synthetic mouse moves to allow extending the
selection by dragging the mouse ouside the display area.  The synthetic
events it generates didn't carry any modifiers, so they were not
properly working when an application had requested mouse tracking
reports.  In that case, generate the events with ShiftModifier, so they
work properly.

src/terminalDisplay/extras/AutoScrollHandler.cpp

@@ -25,11 +25,12 @@ void AutoScrollHandler::timerEvent(QTimerEvent* event)
         return;
     }
 
+    auto* terminalDisplay = static_cast<TerminalDisplay*>(parent());
     QMouseEvent mouseEvent(QEvent::MouseMove,
                            widget()->mapFromGlobal(QCursor::pos()),
                            Qt::NoButton,
                            Qt::LeftButton,
-                           Qt::NoModifier);
+                           terminalDisplay->usesMouseTracking() ? Qt::ShiftModifier : Qt::NoModifier);
 
     QApplication::sendEvent(widget(), &mouseEvent);
 }