Separate reference matrix computation from ImageBasedLighting

[j9liu]

When ImageBasedLighting was introduced in #10226, it included a referenceMatrix getter and setter that was used in recomputing iblReferenceFrameMatrix. However, the referenceMatrix will be different for different models, so if multiple models use the same IBL with different model matrices, the IBL matrix that they use will be incorrect. Instead, models should manage their own iblReferenceFrameMatrix variables.

@ptrgags can you review?

[cesium-concierge]

Thanks for the pull request @j9liu!

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[ptrgags]

@j9liu This change looks good

To test it, I made two sandcastles where an ImageBasedLighting object is shared between multiple models:

• Using Model
• Using ModelExperimental

This branch: (Model on left, ModelExperimental on right)

The key thing is there's a different view of the environment map between the pawns on the ground and the ones floating above them.

One thing I did notice is that the minimumPixelSize gives different results for the two versions of Model, but that's a separate issue.