Fix use of srgb format for texture maps (from glb meshes)

[iche033]

🦟 Bug fix

Summary

Continuing efforts from gazebosim/gz-common#532 for fixing rendering of glb meshes, this PR fixes the texture formats for textures coming from glb meshes. Previous behavior assumes all PBR textures are in sRGB format as the result the meshes are rendered darker than it should be. Only certain textures, (e.g. diffuse, emissive, and lightmap textures) should be in sRGB.

You can test with this water_bottle.sdf world.

Before this change:

After:

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 #931 (868f929) into gz-rendering7 (93841e1) will increase coverage by 0.01%.
The diff coverage is 100.00%.

❗ Current head 868f929 differs from pull request most recent head 2f99c59. Consider uploading reports for the commit 2f99c59 to get more accurate results

@@                Coverage Diff                @@
##           gz-rendering7     #931      +/-   ##
=================================================
+ Coverage          77.22%   77.23%   +0.01%     
=================================================
  Files                170      170              
  Lines              14721    14724       +3     
=================================================
+ Hits               11368    11372       +4     
+ Misses              3353     3352       -1     

Files	Coverage Δ
ogre2/src/Ogre2Material.cc	76.64% <100.00%> (+0.10%)	⬆️

... and 1 file with indirect coverage changes