Return only unique message types in MessageFactory::Types function

[iche033]

🦟 Bug fix

Fixes #470

Summary

The MessageFactory::Type function returns duplicate message types. This is because the list of known message types overlaps with types loaded from descriptor files so the function essentially return two of the same message types. This PR uses a set to filter out duplicates. A potential todo is to return an set instead of a vector.

I also removed an extra duplicate check in the New function (probably leftover from ign -> gz migration)

Checklist

• Signed all commits for DCO
• Added tests
• 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.

[VincidaB]

Still getting ERROR Error: duplicate name 'Distortion' in Namespace .gz.msgs on the web visualization.

[iche033]

Still getting ERROR Error: duplicate name 'Distortion' in Namespace .gz.msgs on the web visualization.

addressed on the gz-launch websocket server side: gazebosim/gz-launch#281

[arilow]

Hi @caguero! Is there anything required to merge this change? Our team is looking forward to being able to use GZweb with Harmonic and this seems the last change required to do that.