Add Private function to world identifier

[nkoenig]

🎉 New feature

Summary

Adds Private functions to WorldIdentifier. This will help facilitate world upload, which is coming in a follow up PR.

Test it

Run the WorldIdentifier_TEST unit tet.

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]

  /github/workspace/include/gz/fuel_tools/WorldIdentifier.hh:159:  Lines should be <= 80 characters long  [whitespace/line_length] [2]