Gaffer 1.3.1.x + Cycles 3.6.0

Please see https://github.com/GafferHQ/gaffer/releases/tag/1.3.1.0

This bundles Cycles 3.6.0 + CUDA + OptiX + HIP as well as the following PRs:
GafferHQ#5101
GafferHQ#5343
GafferHQ#5373
GafferHQ#5396
GafferHQ#5397

Changes from previous build:

• Updated from Gaffer 1.3.0.0 to 1.3.1.0
• Volumes have a useBoundboxMesh setting: https://projects.blender.org/boberfly/cycles/src/branch/volume_boundbox_mesh which will generate a bounding box cube around VDBs instead of a tighter mesh for the goals of preventing voxel-shaped rendering glitches at overlapping points
• Reverted OSL back to 1.12.x, no OSL with OptiX for now - @kubo-von reported issues with OSLObject and OptiX OSL with Cycles seemed to not work correctly in other ways
• Fixed a bug with volume precision presets, it defaults to "Variable", and "Full" is correctly set
• Some small quality of life user-defaults improvements: density and temperature default grid attributes match Blender onto principled_volume, as well as correct default co-ordinates for sky_texture, matching what environment_texture defaults to