Check joint parent link names in Model::Load

[scpeters]

🦟 Bug fix

Fixes #719 on sdf10 (a separate fix is needed for sdf11 and later)

Summary

As noted in #710, several example files in the test/sdf/ folder specify non-existent links in the //joint/parent element, which violates the spec. I added an ign sdf --check test/sdf/joint_axis_infinite_limits.sdf test case in b47f9bf, which properly notes the failure, though the sdf::Root::Load call in INTEGRATION_joint_axis_dom does not report an error. To detect the error in sdf::Root::Load, I added a check in Model::Load that //joint/parent contains a valid link name and fixed the test/sdf/ files in ce8c032.

A different fix will be needed in sdf11 to account for changes in the spec that allow any frame to be named in //joint/parent.

Checklist

• Signed all commits for DCO
• Added tests
• Updated documentation (as needed)
• Updated migration guide (as needed)
• codecheck passed (See contributing)
• All tests passed (See test coverage)
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[codecov-commenter]

Codecov Report

Merging #726 (fa37f00) into sdf10 (a55f9e3) will decrease coverage by 0.05%.
The diff coverage is 100.00%.

❗ Current head fa37f00 differs from pull request most recent head ce8c032. Consider uploading reports for the commit ce8c032 to get more accurate results

@@            Coverage Diff             @@
##            sdf10     #726      +/-   ##
==========================================
- Coverage   87.81%   87.76%   -0.06%     
==========================================
  Files          65       65              
  Lines       10403    10409       +6     
==========================================
  Hits         9135     9135              
- Misses       1268     1274       +6     

Impacted Files	Coverage Δ
src/Model.cc	86.60% <100.00%> (+0.26%)	⬆️
src/ign.cc	70.90% <0.00%> (-1.82%)	⬇️
src/parser.cc	79.22% <0.00%> (-0.56%)	⬇️

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[scpeters]

code coverage is dropping because there is redundant error checking

[azeey]

nit: same comment as the sdf11 PR, not sure if this is necessary since the error is now caught in Model and other tests should already have this file covered.

[scpeters]

as I wrote in #727 (comment), I would keep the test

[osrf-triage]

This pull request has been mentioned on Gazebo Community. There might be relevant details there:

https://community.gazebosim.org/t/new-ignition-releases-2022-03-25-fortress-edifice-citadel/1343/1