Support accessing mutable sensor types

[nkoenig]

🎉 New feature

Summary

I found a need for mutable sensor type accessors while working on sensor editing via the Ignition GUI. I'm putting this into sdf12 because the GUI modifications will be on Fortress, and there would be more work to get this into citadel.

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 #737 (dfa0b04) into sdf12 (c9494fb) will decrease coverage by 0.11%.
The diff coverage is 12.50%.

@@            Coverage Diff             @@
##            sdf12     #737      +/-   ##
==========================================
- Coverage   88.22%   88.11%   -0.12%     
==========================================
  Files          76       76              
  Lines       11437    11457      +20     
==========================================
+ Hits        10090    10095       +5     
- Misses       1347     1362      +15     

Impacted Files	Coverage Δ
src/Sensor.cc	77.32% <12.50%> (-4.10%)	⬇️
src/Utils.hh	94.73% <0.00%> (-2.33%)	⬇️

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[adlarkin]

LGTM - I just have a few comments about the tests. Once those comments are addressed, feel free to merge!