Support FreeGroup features for nested models

[azeey]

🎉 New feature

Summary

This enables FreeGroups to work with nested models

Requires:

• [dartsim] Fix joint construction errors due to link name duplication or BodyNodes moving to other skeletons #220
• [dartsim] Ensure Link and Model APIs continue to work after joint creation in DART #227
• [dartsim] Add empty nested model construction and nested model entity management #228
• [tpe] Add empty nested model construction and nested model entity management #229
• Remove nested models #230

Test it

• Run tests
• Run the nested_models.sdf example world in ign-gazebo and use the transform tool to move the model.
  • ign gazebo --physics-engine ignition-physics-tpe-plugin -v 4 nested_model.sdf
  • ign gazebo --physics-engine ignition-physics-dartsim-plugin -v 4 nested_model.sdf

Before

nested_freegroup_before.mp4

After

nested_freegroup_after.mp4

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

Note to maintainers: Remember to use Squash-Merge

[chapulina]

Removing from beta, this can come in a minor release.

[chapulina]

@azeey , can this be moved from "In progress" to "In review"?

[azeey]

No, this is still in-progress. I'll mark it as draft until it's ready.

[codecov]

Codecov Report

Merging #231 (3e6b658) into ign-physics4 (164f088) will increase coverage by 0.45%.
The diff coverage is 79.31%.

@@               Coverage Diff                @@
##           ign-physics4     #231      +/-   ##
================================================
+ Coverage         75.30%   75.75%   +0.45%     
================================================
  Files               125      125              
  Lines              5463     5503      +40     
================================================
+ Hits               4114     4169      +55     
+ Misses             1349     1334      -15     

Impacted Files	Coverage Δ
tpe/plugin/src/FreeGroupFeatures.cc	65.93% <72.00%> (-1.18%)	⬇️
dartsim/src/FreeGroupFeatures.cc	49.46% <83.87%> (+49.46%)	⬆️
dartsim/src/EntityManagementFeatures.cc	77.48% <100.00%> (ø)
tpe/lib/src/Model.cc	92.78% <100.00%> (ø)

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[chapulina]

Nice, works for me! And I just learned the testing::AssertionFailure() trick to use inside lambdas 👍