Upgrade ign-sensors and support custom sensors

[chapulina]

Part of gazebosim/gz-sensors#18

Summary

Requires gazebosim/gz-plugin#35 and gazebosim/gz-sensors#90.

This is an alternative to #304.

tl;dr: Loading symbols globally is a way of making we find them after they've been registered by another library.

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TODO: write up a summary of what I think is happening.

Test it

• Use all the PRs listed above
• Run worlds that contain sensors, like ign gazebo sensors.sdf or ign gazebo sensors_demo.sdf
• Sensor data should be available through topics, camera images should be visible on widgets

Checklist

• Signed all commits for DCO
• Added tests
• Added example world and/or tutorial
• Updated documentation (as needed)
• Updated migration guide (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

Note to maintainers: Remember to use Squash-Merge

[ahcorde]

I made a comment about the place to change the flag. I tested locally and all system plugins are failing.

Don't merge the other related PR yet until we are sure we can use this solution.

[chapulina]

Removing beta label, we won't have time to wrap this up before code freeze. Let's retarget at Ignition-F.

[ahcorde]

The INTEGRATION_examples_build is failing on MacOS becuase it's not able to find ignition/sensors/Util.hh.

[codecov]

Codecov Report

Merging #617 (341647b) into main (e3ee0af) will decrease coverage by 0.30%.
The diff coverage is 59.15%.

❗ Current head 341647b differs from pull request most recent head bb6b58a. Consider uploading reports for the commit bb6b58a to get more accurate results

@@            Coverage Diff             @@
##             main     #617      +/-   ##
==========================================
- Coverage   64.66%   64.35%   -0.31%     
==========================================
  Files         242      245       +3     
  Lines       19014    19217     +203     
==========================================
+ Hits        12296    12368      +72     
- Misses       6718     6849     +131     

Impacted Files	Coverage Δ
include/ignition/gazebo/Link.hh	100.00% <ø> (ø)
include/ignition/gazebo/Server.hh	100.00% <ø> (ø)
include/ignition/gazebo/rendering/RenderUtil.hh	100.00% <ø> (ø)
src/SdfEntityCreator.cc	84.53% <0.00%> (-0.89%)	⬇️
src/gui/Gui.cc	65.35% <ø> (+0.23%)	⬆️
src/gui/GuiRunner.cc	85.91% <0.00%> (-0.34%)	⬇️
src/gui/plugins/scene3d/Scene3D.cc	10.83% <ø> (+0.01%)	⬆️
src/systems/log/LogRecord.cc	80.56% <ø> (-0.31%)	⬇️
src/rendering/RenderUtil.cc	34.67% <14.28%> (-0.17%)	⬇️
src/systems/physics/Physics.cc	70.27% <20.00%> (-0.20%)	⬇️
... and 22 more

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[chapulina]

The 23 test failures on Jenkins Ubuntu are due to gazebo-tooling/release-tools#494 and can be ignored for now. #971 should fix them if we don't fix it in the infra. The rest of CI looks good. Merging!