Populate joint forces through physics

[vatanaksoytezer]

🎉 New feature

Closes #883

Summary

Exports joint forces through physics.cc to enable force-torque sensors and efforts through joint state publisher.

Test it

• Pull [dart] Compute Inverse Dynamics for all skeletons to populate joint forces gz-physics#143 and this PR.
• Open up any world file with joint_state_publisher plugin (for eg. lift_drag.sdf)
• Listen the joint_states topic through ros2 bridge or Ignition

Checklist

• Signed all commits for DCO
• Added tests
• Added example and/or tutorial
• Updated documentation (as needed)
• Updated migration guide (as needed)
• 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

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[azeey]

Just wanted to say that I'm not sure if we have consensus on whether gazebosim/gz-physics#143 (computing inverse dynamics) is how we'll obtain joint forces, so it might take some time before we can merge this PR.

[vatanaksoytezer]

Just wanted to say that I'm not sure if we have consensus on whether ignitionrobotics/ign-physics#143 (computing inverse dynamics) is how we'll obtain joint forces, so it might take some time before we can merge this PR.

@azeey I think regardless of gazebosim/gz-physics#143 getting merged, this PR would still be necessary in any implementation for calculating joint forces.

Regardless, gazebosim/gz-physics#143 seemed pretty fast to me in calculating inverse dynamics for 25 joints in a very complex scenario. I was around 95-99% real time all the time with a moderate gaming PC (i7 9750H + 1660Ti) in that simulation. Let me know if there are any tests you would like me to do to compare performances or help choose the right implementation.

I strongly think joint forces would be pretty helpful for other people using the simulation, whether to debug or use them in their calculations. So, I would love help get these merged and ready do some tests / more PRs towards it.

[vatanaksoytezer]

Closing since I believe this won't be merged in favor of other implementation that is merged in Fortress. Though as of my testing I can't read efforts / forces through joint states in fortress binaries.

[chapulina]

Though as of my testing I can't read efforts / forces through joint states in fortress binaries.

We should make sure that this works. Maybe capture it in an issue that we look into soon?