Extend Chiang tests across languages

[jstone-lucasfilm]

This changelist extends testing of Chiang Hair BSDF nodes across shading languages, allowing render comparisons to include the complete Examples and TestSuite folders.

In order to avoid shader compilation errors, placeholder OSL implementations of these nodes have been added, and these should be replaced with accurate implementations once they are supported.

[jstone-lucasfilm]

Here's a new GLSL/OSL comparison with the changes in this PR:

MaterialXRenderTests_11_02_2024.pdf

[ld-kerley]

What's the benefit here to running the tests with a place holder implementation - instead of just skipping the tests?

With a missing implementation, if someone tries to use it they will get a meaningful error - instead of just an incorrect image, which may or may not be caught.

[jstone-lucasfilm]

@ld-kerley That's the approach we've taken with previous MaterialX nodes, where we allow our render test suite to run without failures, even when individual features aren't yet implemented in every language that we're testing (e.g. thin-film interference in OSL, surface displacement in GLSL, and so forth).

It's worth discussing whether we can propose a better approach going forward, but this is the approach that we've used historically when developing new MaterialX nodes, where implementations across languages are usually staggered in time.