Fix initialization of world components when enabling velocity checks (backport #2777)

[mergify]

🦟 Bug fix

Fixes #2774

Summary

When using the link API to enable velocity checks for a link that does not yet have the world ECM components (WorldPose, WorldLinearVelocity, WorldAngularVelocity), typically before the physics system plugin does its first update loop, such components will be initialized with their default constructor, zeroing values that might not be zero. One more evident example is the link world pose that could have already been initialized.

1. Add the same unit test added by this MR to gz-sim/src/Link_TEST.cc
2. Build the package: colcon build --packages-select gz-sim9
3. Execute the test from your build folder: ./bin/UNIT_Link_TEST --gtest-filter=*EnableVelocityChecks*
4. You should verify the tests will fail because all world components are zero

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.

---

This is an automatic backport of pull request #2777 done by [Mergify](https://mergify.com).

[mergify]

Cherry-pick of 4ae75e5 has failed:

On branch mergify/bp/gz-sim8/pr-2777
Your branch is up to date with 'origin/gz-sim8'.

You are currently cherry-picking commit 4ae75e5b.
  (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:   include/gz/sim/Util.hh
	modified:   src/Link.cc
	modified:   src/Link_TEST.cc
	modified:   src/Util_TEST.cc

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   test/integration/mesh_inertia_calculation.cc

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

[gabrielfpacheco]

@scpeters, thanks for triggering the automatic creation of this backport PR. There is a simple conflict to be solved in test/integration/mesh_inertial_calculation.cc, though.

How should we proceed in this case? I don't have the permission to update this branch, but I can create a new PR if this is the right process.

[scpeters]

@scpeters, thanks for triggering the automatic creation of this backport PR. There is a simple conflict to be solved in test/integration/mesh_inertial_calculation.cc, though.

How should we proceed in this case? I don't have the permission to update this branch, but I can create a new PR if this is the right process.

I resolved conflicts and amended the commit

[gabrielfpacheco]

Thanks a lot, guys!