Draft: Parser warning message when <gazebo> reference does not exist in URDF

[aagrawal05]

🎉 New feature

Closes #1372

Summary

Added functionality to emit a warning when a reference to a link does not exists by adding a check in the InsertSDFExtensionLink method.

Test it

I've added the ParseGazeboRefDoesntExistWarningMessage test which adds the test case mentioned from #1372 with conflicting U+0069 and U+0456 characters.

Checklist

• Signed all commits for DCO
• Added tests
• Added example and/or tutorial
• Updated documentation (as needed)
• Updated migration guide (as needed)
• Consider updating Python bindings (if the library has them)
• codecheck passed (See contributing)
• All tests passed (See test coverage)
• While waiting for a review on your PR, please help review another open pull request to support the maintainers

Note to maintainers: Remember to use Squash-Merge and edit the commit message to match the pull request summary while retaining Signed-off-by messages.

[ahcorde]

If you check the diff, the indentation in your changes is very wierd. Do you mind to fix it ?

[aagrawal05]

If you check the diff, the indentation in your changes is very wierd. Do you mind to fix it ?

Hi, I took a look at it—I think there was something wrong with my text editor, it showed a different output and I hadn't noticed earlier. Let me fix it now.

[aagrawal05]

Ok, sorry about the many commits—I think the formatting should be fixed now. I'll make sure everything fits with rigorously with codecheck afterwards.