bullet-featherstone: Fix attaching fixed joint between models with inertial pose offset

[iche033]

🦟 Bug fix

Summary

When creating a fixed constraint between links, the SetJointTransformFromParent currently does not take into account the inertial pose. If an inertial pose offset exists, the fixed constraint causes the 2 models to be displaced from their original position. This PR updates the calculation in SetJointTransformFromParent to include inertial pose offset.

The detachable_joint.world test world is updated to use a model with inertial pose offset - this world is used by the CorrectAttachmentPoints test in detachable_joint common test. The test fails without the changes in this PR.

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)
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[azeey]

Great find!