[dartsim] Add support for joint frame semantics

[azeey]

🎉 New feature

Summary

Since joints in DART are not considered frames, this adds dart::dynamics::SimpleFrame attached to the child body of a joint and offset from the child by the pose of the joint.

Test it

Run UNIT_KinematicsFeatures_TEST

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

[scpeters]

nit: rename the test KinematicsFeaturs_TEST.cc -> KinematicsFeatures_TEST.cc

otherwise looks good

[codecov]

Codecov Report

Merging #288 (5f2bbe2) into ign-physics2 (347f082) will decrease coverage by 0.05%.
The diff coverage is 66.66%.

@@               Coverage Diff                @@
##           ign-physics2     #288      +/-   ##
================================================
- Coverage         83.21%   83.16%   -0.06%     
================================================
  Files               106      106              
  Lines              4040     4051      +11     
================================================
+ Hits               3362     3369       +7     
- Misses              678      682       +4     

Impacted Files	Coverage Δ
dartsim/src/KinematicsFeatures.cc	72.00% <50.00%> (-11.34%)	⬇️
dartsim/src/Base.hh	99.01% <100.00%> (+0.04%)	⬆️

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[azeey]

nit: rename the test KinematicsFeaturs_TEST.cc -> KinematicsFeatures_TEST.cc

Done in 96298c4

[scpeters]

out of curiosity, I ran the test with the changes to Base.hh reverted and got an exception somewhere:

[ RUN      ] KinematicsFeaturesFixture.JointFrameSemantics
unknown file: Failure
C++ exception with description "unordered_map::at: key not found" thrown in the test body.
[  FAILED  ] KinematicsFeaturesFixture.JointFrameSemantics (83 ms)

With --gtest_catch_exceptions=0, I was able to get a backtrace implicating this line in KinematicsFeatures::SelectFrame. If you think it would be easy to improve the console output in this situation and worth fixing now, then go ahead, but otherwise it's fine as is

[azeey]

out of curiosity, I ran the test with the changes to Base.hh reverted and got an exception somewhere:

[ RUN      ] KinematicsFeaturesFixture.JointFrameSemantics
unknown file: Failure
C++ exception with description "unordered_map::at: key not found" thrown in the test body.
[  FAILED  ] KinematicsFeaturesFixture.JointFrameSemantics (83 ms)

With --gtest_catch_exceptions=0, I was able to get a backtrace implicating this line in KinematicsFeatures::SelectFrame. If you think it would be easy to improve the console output in this situation and worth fixing now, then go ahead, but otherwise it's fine as is

I added a console message and an assertion in 5f2bbe2 following the pattern that was already there in KinematicsFeatures.cc.