This splits the volume related data (properties for rendering and attributes) of the Mesh node
into a new Volume node type.

This Volume node derives from the Mesh class since we generate a mesh for the bounds of the
volume, as such we can safely work on Volumes as if they were Meshes, e.g. for BVH creation.
However such code should still check for the geometry type of the object to be MESH or VOLUME
which may be bug prone if this is forgotten.

This is part of T79131.