Add "ChangedWorldPose" to ForwardStep::Output's expected data

[adlarkin]

Signed-off-by: Ashton Larkin ashton@openrobotics.org

🎉 New feature

Related to #223

Possible solution for #219

Summary

#223 added functionality to DART and TPE to write changed link data from an iteration to ForwardStep::Output so that downstream libraries like ign-gazebo can use this data for more efficient post-physics processing/updates (gazebosim/gz-sim#678). In order for downstream libraries to make this functionality optional, the changed link data that is written to by DART and TPE must be of type ExpectedData instead of RequiredData (that way, downstream libraries can see if this data was actually written to or not). This PR makes this change.

Test it

Using this PR with gazebosim/gz-sim#678, users can run the ign-gazebo physics system integration test. This will use the output link data that ign-physics writes to in order to update the simulation state in ign-gazebo. All checks in the integration test should pass.

Users can then check out DART and TPE before these engines were modified to write output data (commit 109de85):

cd ign-physics
git checkout 109de85 -- dartsim/ tpe/

Re-run the physics integration test. This will use data internal to ign-gazebo (a local link pose cache in combination with the EntityComponentManager) to update the simulation state. All checks in the integration test should pass.

If you'd like to verify that the steps I described above use both data written to from ign-physics and data internal to ign-gazebo, you can add some print statements in each if/else block here to see what is being called.

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

[adlarkin]

@azeey, just a few questions for you about the implementation.

[codecov]

Codecov Report

Merging #238 (78b8ec0) into main (246909b) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main     #238   +/-   ##
=======================================
  Coverage   83.15%   83.15%           
=======================================
  Files         107      107           
  Lines        4221     4221           
=======================================
  Hits         3510     3510           
  Misses        711      711           

Impacted Files	Coverage Δ
include/ignition/physics/ForwardStep.hh	100.00% <ø> (ø)
dartsim/src/SimulationFeatures.cc	91.22% <100.00%> (ø)
tpe/plugin/src/SimulationFeatures.cc	78.33% <100.00%> (ø)

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[azeey]

LGTM!