Split ROS 1 -> 2 C++ page into a reference page and a tutorial page (backport #4779)

[mergify]

This splits the C++ ROS 1 to 2 migration page into two pages:

• A tutorial page, which is good for beginners to migrating from ROS 1 to ROS 2
• A reference page, which is good for someone actively migrating their package and wanting to CTRL+F how to do something

The tutorial content is unchanged except for:

• Added an intro, prerequisites, and conclusion sections
• Removed the sections about how to build and run the ROS 1 code because it's not easy to require both a working ROS 1 and a working ROS 2 installation on the same machine
• Changed ^^^^ to ---- in a couple headings to put them on the same level as Prerequisites.

  ---

  This is an automatic backport of pull request Split ROS 1 -> 2 C++ page into a reference page and a tutorial page #4779 done by Mergify.

[mergify]

Cherry-pick of 4e7e865 has failed:

On branch mergify/bp/humble/pr-4779
Your branch is up to date with 'origin/humble'.

You are currently cherry-picking commit 4e7e8658.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Changes to be committed:
	modified:   source/How-To-Guides/Migrating-from-ROS1.rst
	new file:   source/How-To-Guides/Migrating-from-ROS1/Migrating-CPP-Package-Example.rst

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

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/11133997089/artifacts/2003232600.

To view the resulting site:

1. Click on the above link to download the artifacts archive
2. Extract it
3. Open html-artifacts-4794/index.html in your favorite browser