Fix memory leak in ImageDisplay.cc

[darksylinc]

Summary

Note: This is a big memory leak in the order of 30 MB/s or more depending on many conditions; thus it should be prioritized. A 32GB RAM machine can run out of memory after approximately 20 min of real time simulation.

I don't like the interface of common::Image outputting a raw pointer that is deleted if the input is non-nullptr but it is up to the caller to the delete if it's not called again. And it's not documented either.
I don't like the amount of unnecessary copies required by ImageDisplay::ProcessImage either. Or the fact that we do one allocation per frame (instead of trying to keep an allocated region while in use).

But all those are problems for another day.

Don't forget to merge this to ign-gui5 and later :)

🦟 Bug fix

Fixes gazebosim/gz-sim#1011

Checklist

• Signed all commits for DCO
• Added tests
• 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

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[codecov]

Codecov Report

Merging #287 (6ed0d91) into ign-gui4 (33edc9e) will decrease coverage by 0.02%.
The diff coverage is 0.00%.

❗ Current head 6ed0d91 differs from pull request most recent head 6d7e66d. Consider uploading reports for the commit 6d7e66d to get more accurate results

@@             Coverage Diff              @@
##           ign-gui4     #287      +/-   ##
============================================
- Coverage     66.39%   66.37%   -0.03%     
============================================
  Files            26       26              
  Lines          3205     3206       +1     
============================================
  Hits           2128     2128              
- Misses         1077     1078       +1     

Impacted Files	Coverage Δ
src/plugins/image_display/ImageDisplay.cc	30.08% <0.00%> (-0.25%)	⬇️

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[chapulina]

Thanks for the fix!

[osrf-triage]

This pull request has been mentioned on Gazebo Community. There might be relevant details there:

https://community.gazebosim.org/t/new-ignition-releases-2022-01-10/1228/1