Cycles: Add dispersion to Principled BSDF

Dispersion is defined by two parameters:
Abbe Number and Dispersion Scale.

This corresponds to OpenPBR v1.1.1

Pull Request: https://projects.blender.org/blender/blender/pulls/162041

Note: dispersion is temporarily disabled when using MNEE (shadow caustics) on oneAPI, due to a compiler bug. Waiting for a fix from the oneAPI side.

![prism.png](/attachments/219c3966-b39d-4846-991b-976f84f83081)
Co-authored-by: Sebastian Herholz <sebastian.herholz@gmail.com>

tests/python/eevee_render_tests.py

@@ -433,6 +433,9 @@ def main():
         # principled_bsdf_thinfilm_metallic has some weird behavior in reflection of
         # black surfaces. to be investigated
         report.set_fail_percent(0.09)
+        # principled_bsdf_dispersion has some difference in the highlights
+        if gpu_vendor == "AMD":
+            report.set_fail_threshold(6.0 / 255.0)
     elif test_dir_name.startswith('integrator'):
         # Noise difference in transparent materials (mostly transparent_spatial_splits)
         report.set_fail_threshold(8.0 / 255.0)

tests/python/storm_render_tests.py

@@ -48,6 +48,8 @@ BLOCKLIST_HYDRA = [
     "osl_camera_.*.blend",
     # The result doesn't match storm-usd
     "many_lights.blend",
+    # The result differs between platforms
+    "principled_bsdf_dispersion.blend",
 ]
 
 BLOCKLIST_USD = [
@@ -66,6 +68,8 @@ BLOCKLIST_USD = [
     "principled_bsdf_thin_glass.blend",
     # Custom OSL camera not supported.
     "osl_camera_.*.blend",
+    # The result in incorrect
+    "principled_bsdf_dispersion.blend",
 ]
 
 # Metal support in Storm is no as good as OpenGL, though this needs to be