Fix OGRE 2 with VirtualGL

[peci1]

🦟 Bug fix

Fixes #526 and maybe gazebosim/gz-sim#1746 .

Summary

Restore GLX context after loading the OGRE plugin. It is possible the loading process changes the current GLX context.

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 #794 (a9634c6) into ign-rendering6 (74d8c78) will increase coverage by 0.01%.
The diff coverage is 100.00%.

❗ Current head a9634c6 differs from pull request most recent head 2f18450. Consider uploading reports for the commit 2f18450 to get more accurate results

@@                Coverage Diff                 @@
##           ign-rendering6     #794      +/-   ##
==================================================
+ Coverage           77.81%   77.83%   +0.01%     
==================================================
  Files                 146      146              
  Lines               13412    13416       +4     
==================================================
+ Hits                10437    10442       +5     
+ Misses               2975     2974       -1     

Impacted Files	Coverage Δ
ogre2/src/Ogre2RenderEngine.cc	78.49% <100.00%> (+0.19%)	⬆️
...e/ignition/rendering/base/BaseGaussianNoisePass.hh	100.00% <0.00%> (+3.33%)	⬆️

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[peci1]

I've tested this PR with all the combinations I could test - (Gazebo server with rendering sensors | Gazebo client) X (Gazebo rendering via GLX | Gazebo rendering via EGL (--headless-rendering) ) X (direct HW accelerated rendering | direct SW rendering (xvfb-run -a) | VirtualGL faking via GLX | VirtualGL faking via HW-accelerated EGL | VirtualGL faking via Mesa software EGL renderer).

[iche033]

Thanks for the fix! I think something was went wrong on the homebrew build. Retriggered a new one.

[iche033]

builds looks good