Added accessor for kinematics from MocoInverse init

[AllisonJohn]

Fixes issue #3646

Brief summary of changes

Allows users to get the kinematics which are removed from the study if they need to add them back to the solution

Testing I've completed

Tested the forum example, exampleMocoInverse.cpp solveMocoInverseWithEMG() but with
TimeSeriesTable kinematics = inverse.initializeKinematics();
after making the MocoStudy and

solution.insertStatesTrajectory(kinematics);

std::vector<std::string> outputPaths;
outputPaths.push_back(".*tendon_force");
TimeSeriesTable outputs = study.analyze(solution, outputPaths);
OpenSim::STOFileAdapter::write(outputs, "tendon_forces_withEMG.sto");

after getting the MocoSolution, which previously failed without inserting kinematics.

testMocoInverse still works, added a section for initializeKinematics.

Looking for feedback on...

CHANGELOG.md (choose one)

• updated.

---

This change is 

[nickbianco]

Reviewed 4 of 4 files at r1, all commit messages.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on @AllisonJohn)

[nickbianco]

Windows failure is unrelated. Merging.