OpenVDB Points Rendering

The points node has new parameters for loading points from a points grid in an OpenVDB file. At a minimum, you must set the file_name and file_grid parameters to load an OpenVDB file. Arnold tries to guess the point attributes for position, radius and velocity, but these attributes from the grid can be specified directly if needed. All other point attributes that reasonably map to Arnold data types are available to shaders as user data. Note that not all Arnold plugins expose the points node. (ARNOLD-15663)