RenderWindow instead of RenderPanel

[JaehyunShim]

To use the package in this repository, you should use the getRenderPanel() function which OSRF has not added to Rviz2 yet. I mentioned it and asked them to add it to Rviz2 in the following link.

ros2/rviz#664 (comment)

Even if they do not add it, you can still do a very similar thing by using below instead of (https://github.com/MartiBolet/Custom_Qt5_Rviz2/blob/main/src/myviz.cpp#L48).

main_layout->addWidget(QWidget::createWindowContainer(frame_->getRenderWindow()));

In this case, the app will be viewing the RenderWindow inside the RenderPanel instead.