Fix Pattern Editor Not Updating (#8175)

The TrackContentWidgets in the pattern editor rely on the positionChanged signal to be sent when the pattern index changes so that they know when to update. This signal was removed in #7454, but this PR puts it back.

src/gui/editors/PatternEditor.cpp

@@ -198,6 +198,7 @@ void PatternEditor::updatePosition()
 	{
 		trackView->update();
 	}
+	emit positionChanged(m_currentPosition);
 }
 
 void PatternEditor::updatePixelsPerBar()