Polish the ROS 1 -> 2 CMake instructions (backport #4767)

[mergify]

This updates the CMake portion of the ROS 1 to ROS 2 guide, and fixes one bug in the C++ code

• Included links to real examples in the core (Mostly tf2)
• Updated section headings to CMakeLists.txt steps appear in the ToC
• Used modern CMake targets instead of standard CMake variables
• Used Active voice and second person perspective
• Removed unnecessary code from example code in Unit tests section
• Make the example package.xml start with format 2 since that's different from migrating from ROS 1 to ROS 2.

C++ bug fix: use ->publish( instead of .publish(

I have tried out all steps of the example part of the guide to make sure they work.

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This is an automatic backport of pull request #4767 done by [Mergify](https://mergify.com).

[mergify]

Cherry-pick of 9d6552c has failed:

On branch mergify/bp/iron/pr-4767
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You are currently cherry-picking commit 9d6552c0.
  (fix conflicts and run "git cherry-pick --continue")
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  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   source/How-To-Guides/Migrating-from-ROS1/Migrating-CPP-Packages.rst

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To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally

[github-actions]

HTML artifacts: https://github.com/ros2/ros2_documentation/actions/runs/11111498343/artifacts/1996947739.

To view the resulting site:

1. Click on the above link to download the artifacts archive
2. Extract it
3. Open html-artifacts-4776/index.html in your favorite browser