Unload render engine when the sensors system exits

[iche033]

🦟 Bug fix

Fixes #1410

Depends on:

• Cleanup resources in CameraSensor destructor gz-sensors#340
• Fix deleting ogre2 when created (and deleted) in a thread gz-rendering#840

Summary

The render engine is never destroyed / unloaded when the server shuts down. This leads to issues such as memory leak and not being able to relaunch the server with the sensors system, e.g. as seen in #1410, rendering tests n gz-sim can not be run one after another in the same process.

This PR adds a function in RenderUtil to destroy the scene and unload the engine.

To test:

Run the PERFORMANCE_sensors_system test that repeatedly launches the server with the sensors system.

Note that to run the tests, you'll need the above PRs in gz-rendering and gz-sensors otherwise gz will crash.

Checklist

• Signed all commits for DCO
• Added tests
• 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 #1960 (e26e577) into gz-sim7 (0742968) will decrease coverage by 0.07%.
The diff coverage is 77.30%.

@@             Coverage Diff             @@
##           gz-sim7    #1960      +/-   ##
===========================================
- Coverage    65.08%   65.02%   -0.07%     
===========================================
  Files          352      352              
  Lines        28312    28393      +81     
===========================================
+ Hits         18428    18463      +35     
- Misses        9884     9930      +46     

Impacted Files	Coverage Δ
include/gz/sim/rendering/MarkerManager.hh	100.00% <ø> (ø)
include/gz/sim/rendering/RenderUtil.hh	100.00% <ø> (ø)
include/gz/sim/rendering/SceneManager.hh	100.00% <ø> (ø)
src/SimulationRunner.hh	100.00% <ø> (ø)
...rc/systems/ackermann_steering/AckermannSteering.hh	100.00% <ø> (ø)
include/gz/sim/EventManager.hh	75.75% <66.66%> (-3.41%)	⬇️
src/systems/sensors/Sensors.cc	62.74% <70.93%> (-0.27%)	⬇️
...rc/systems/ackermann_steering/AckermannSteering.cc	80.09% <73.52%> (-0.45%)	⬇️
src/SimulationRunner.cc	91.63% <100.00%> (-0.27%)	⬇️
src/rendering/MarkerManager.cc	14.81% <100.00%> (+1.78%)	⬆️
... and 2 more

... and 1 file with indirect coverage changes

[mjcarroll]

I think this is still failing PERFORMANCE_sensors_system on the buildfarm, so it may need another look.

[iche033]

I think this is still failing PERFORMANCE_sensors_system on the buildfarm, so it may need another look.

removed bad ifdef logic in e26e577, which should hopefully fix it.

[iche033]

ubuntu build fixed