Fix deleting ogre2 when created (and deleted) in a thread

[iche033]

🦟 Bug fix

Summary

I ran into a crash in gz-sim on exit after unloading the ogre2 render engine. It was found that it only happens if ogre-next is built with EGL support and the engine is created / deleted in a thread. The fix is to make sure EGL returns to its original state, specifically by calling eglReleaseThread() after deleting ogre root.

The fix this PR make EGL calls which requires including and linking against the EGL library, hence the extra cmake code. The proper fix may be to do this inside ogre.

To Test:

Run the INTEGRATION_load_unload test

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 #840 (9062d6f) into gz-rendering7 (c2e72ee) will increase coverage by 0.00%.
The diff coverage is 91.66%.

❗ Current head 9062d6f differs from pull request most recent head f6e2798. Consider uploading reports for the commit f6e2798 to get more accurate results

@@              Coverage Diff               @@
##           gz-rendering7     #840   +/-   ##
==============================================
  Coverage          77.37%   77.37%           
==============================================
  Files                164      164           
  Lines              14456    14460    +4     
==============================================
+ Hits               11185    11189    +4     
  Misses              3271     3271           

Impacted Files	Coverage Δ
ogre2/src/Ogre2RenderEngine.cc	76.13% <91.66%> (+0.18%)	⬆️

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[azeey]

Not sure if this should've been merged with the homebrew failures. The stable branch is green https://build.osrfoundation.org/view/ign-garden/job/ignition_rendering-ci-gz-rendering7-homebrew-amd64/

[iche033]

testing changes in #841 to see if it fixes the crash on macOS