Model actor toelement functions

[nkoenig]

🎉 New feature

Summary

Adds ToElement functions for Model and `Actor.

Test it

Run the tests.

Checklist

• Signed all commits for DCO
• Added tests
• Updated documentation (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

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[codecov-commenter]

Codecov Report

Merging #782 (0aea6a4) into sdf12 (5b48e41) will decrease coverage by 0.01%.
The diff coverage is 82.50%.

@@            Coverage Diff             @@
##            sdf12     #782      +/-   ##
==========================================
- Coverage   89.32%   89.31%   -0.02%     
==========================================
  Files          76       76              
  Lines       12415    12495      +80     
==========================================
+ Hits        11090    11160      +70     
- Misses       1325     1335      +10     

Impacted Files	Coverage Δ
src/Model.cc	89.56% <80.00%> (-0.75%)	⬇️
src/Actor.cc	92.73% <83.63%> (-0.41%)	⬇️

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[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-2022-04-13-fortress-edifice/1367/1