Add Light class

[iche033]

🎉 New feature

Part of #325

Summary

Add Light class to help ease migration from classic

Test it

Run the UNIT_Light_TEST and INTEGRATION_light tests

Checklist

• Signed all commits for DCO
• Added tests
• Added example and/or tutorial
• Updated documentation (as needed)
• Updated migration guide (as needed)
• Consider updating Python bindings (if the library has them)
• 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 and edit the commit message to match the pull request summary while retaining Signed-off-by messages.

[codecov]

Codecov Report

Merging #1918 (a8f4bb1) into ign-gazebo6 (89df3b7) will increase coverage by 0.23%.
The diff coverage is 92.43%.

@@               Coverage Diff               @@
##           ign-gazebo6    #1918      +/-   ##
===============================================
+ Coverage        64.99%   65.22%   +0.23%     
===============================================
  Files              324      326       +2     
  Lines            26562    26813     +251     
===============================================
+ Hits             17264    17490     +226     
- Misses            9298     9323      +25     

Impacted Files	Coverage Δ
src/Sensor.cc	85.71% <85.71%> (ø)
src/Light.cc	93.11% <93.11%> (ø)
src/Joint.cc	97.10% <100.00%> (+0.10%)	⬆️
src/SimulationRunner.cc	90.82% <0.00%> (-0.95%)	⬇️

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