Remove detachable joints when a model is removed

[iche033]

🦟 Bug fix

Partially fixes #2624

Summary

Remove detachable joints from the ECM when a model is removed. The physics engine will then also remove any associated detachable joint physics objects. I also made a change in physics system to let physics engine remove the detachable joints first before models.

Now when you delete a model, the detachable joints should be deleted causing objects to be detached.

To test:

launch detachable_joint.sdf world

gz sim -v 4 -r ./src/gz-sim/examples/worlds/detachable_joint.sdf

Delete vehicle_blue and the breadcrumbs should now fall to the ground.

Try resetting the world it should no longer crash (#2624). However, the breadcrumbs remain detached, which I think it's a separate issue related to reset.

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.