Add support for volume (OpenVDB) USD export:
- Allows to export both static and animated volumes.
- Supports volumes that have OpenVDB data from files or are generated in
Blender with 'Mesh to Volume' modifier.
- For volumes that have generated data in Blender it also exports
corresponding .vdb files. Those files are saved in a new folder named
"volumes".
- Slightly changes the USD export UI panel. "Relative Texture Paths"
becomes "Relative Paths" (and has separate UI box) as the
functionality will now apply to both textures and volumes. Disabling
of this option due to "Materials" checkbox being turned off has been
removed.
Reviewed By: sybren, makowalski
Differential Revision: https://developer.blender.org/D14193
Manifest Task: T95407
Piotr Makal
ce3dd12371