Also see #103343.
There was one unusual complication due to `openvdb` here. The `BKE_volume.h`
header included `openvdb` but that would not link correctly in rna code. I'm not entirely
sure why any of the openvdb code is actually instantiated, may be an issue in the
`openvdb` headers. The solution is to create a new header that gives access to the
underlying `openvdb` data structure for a `Volume` geometry. This header can't be
included in rna for now, until the linking issues are resolved.
Pull Request: https://projects.blender.org/blender/blender/pulls/109508
422e0c02e9