Add support for lightmaps in ogre2

[iche033]

depends on gazebosim/gz-common#132

main changes:

• updated mesh factory to create mesh with multiple texture coordinate sets
• added lightmap APIs to Material - users can choose which texture coordinate set to use for the lightmap
• To keep things simple, lightmap is currently blended with the base albedo map using the Overlay bend mode (here's a description of the different blend modes).
• fixed a transparency issue that happens when a grayscale albedo map is used.

[chapulina]

@osrf-jenkins run tests please 🙏

[chapulina]

Ah no, triggered too soon 🤦‍♀️

[chapulina]

I fixed code check and a failing test on 1d69e73.

@iche033 , I removed a big chunk of code from the test which didn't seem to be used. Please check if that was indeed unnecessary and if it was ok to remove it.

[codecov]

Codecov Report

Merging #182 (0d62019) into main (d4406e1) will increase coverage by 0.05%.
The diff coverage is 75.00%.

@@            Coverage Diff             @@
##             main     #182      +/-   ##
==========================================
+ Coverage   53.03%   53.08%   +0.05%     
==========================================
  Files         143      143              
  Lines       13505    13545      +40     
==========================================
+ Hits         7163     7191      +28     
- Misses       6342     6354      +12     

Impacted Files	Coverage Δ
include/ignition/rendering/Material.hh	100.00% <ø> (ø)
include/ignition/rendering/base/BaseMaterial.hh	60.44% <23.07%> (-1.91%)	⬇️
ogre2/src/Ogre2Material.cc	95.13% <92.59%> (-0.30%)	⬇️
ogre2/src/Ogre2MeshFactory.cc	83.45% <100.00%> (+0.12%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update d4406e1...0d62019. Read the comment docs.

[iche033]

I removed a big chunk of code from the test which didn't seem to be used. Please check if that was indeed unnecessary and if it was ok to remove it.

actually the test was supposed to test and verify copying from this common::Material but it was doing a CopyFrom from the wrong material variable. I've updated the test in 0d62019.