Add RViz Marker tutorials (backport #6476)

[mergify]

Description

I finally got around to continuing the effort of adding and migrating the old RViz tutorials from the old RViz documentation page.

In the abandoned PR #3908, we agreed to first add the RViz User Guide and Marker: Display Types tutorials. Those were added in #4040 and #4821. This PR adds the next two marker tutorials:

• Marker: Sending Basic Shapes (C++)
• Marker: Points and Lines (C++)

A few notes and assumptions:

• I kept the structure close to the old wiki.ros.org tutorials, as we did for the two tutorials that have already been merged. I also used the .rst files in visualization_tutorials as additional inspiration.
• I changed the order of the tutorials on the main RViz subpage. I think it makes sense for the User Guide and Marker tutorial series to appear before the custom Panel and Display tutorials, since they are more fundamental and easier to approach. I think this make the page progress more naturally in difficulty.
• I included both marker tutorials in one PR because they are closely related. If preferred, I can split them into separate PRs.
• I also have the next Interactive Marker tutorial series mostly ready, but I would like to get this PR merged first.

Finishing the remaining Marker tutorials seems worthwhile, and migrating or adding the three Interactive Marker tutorials would also be very helpful for new user IMO. The old wiki.ros.org tutorials are well written, and visualization_tutorials already provides maintained code for them.

Did you use Generative AI?

Yes. GPT-5.4 was used only for textual improvements to the tutorials’ explanations and structure.

As described in the tutorials themselves, all code in these tutorials comes from visualization_tutorials, not from generative AI.

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This is an automatic backport of pull request #6476 done by Mergify.

[github-actions]

HTML artifacts: https://github.com/ros2/ros2_documentation/actions/runs/25117726062/artifacts/6711040304.

To view the resulting site:

1. Click on the above link to download the artifacts archive
2. Extract it
3. Open html-artifacts-6483/index.html in your favorite browser