Bullet-featherstone: Apply external forces and torques

[mjcarroll]

🎉 New feature

Closes #

Summary

Test it

Checklist

• Signed all commits for DCO
• Added tests
• Added example and/or tutorial
• 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.

[codecov]

Codecov Report

Merging #438 (da1d494) into add-bullet-featherstone (9e7af39) will increase coverage by 0.80%.
The diff coverage is 62.70%.

❗ Current head da1d494 differs from pull request most recent head 7a4adef. Consider uploading reports for the commit 7a4adef to get more accurate results

@@                     Coverage Diff                     @@
##           add-bullet-featherstone     #438      +/-   ##
===========================================================
+ Coverage                    74.55%   75.36%   +0.80%     
===========================================================
  Files                          128      140      +12     
  Lines                         5628     7066    +1438     
===========================================================
+ Hits                          4196     5325    +1129     
- Misses                        1432     1741     +309     

Impacted Files	Coverage Δ
bullet-featherstone/src/FreeGroupFeatures.cc	0.00% <0.00%> (ø)
bullet/src/JointFeatures.cc	0.00% <0.00%> (ø)
bullet/src/SDFFeatures.cc	51.03% <0.00%> (+5.97%)	⬆️
dartsim/src/SimulationFeatures.cc	93.44% <ø> (+3.27%)	⬆️
dartsim/src/SimulationFeatures.hh	100.00% <ø> (ø)
include/gz/physics/ForwardStep.hh	100.00% <ø> (ø)
include/gz/physics/FrameID.hh	100.00% <ø> (ø)
include/gz/physics/FrameSemantics.hh	100.00% <ø> (ø)
include/gz/physics/Geometry.hh	100.00% <ø> (ø)
include/gz/physics/detail/FrameSemantics.hh	95.91% <0.00%> (-4.09%)	⬇️
... and 38 more

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