This adds a Mesh To Volume Node T86838 based on the existing modifier. The mesh to volume conversion is implemented in the geometry module, and shared between the node and the modifier. Currently the node outputs a grid with the name "density". This may change in the future depending on the decisions made in T91668. The original patch was by Kris (@Metricity), further implementation by Geramy Loveless (@GeramyLoveless), then finished by Erik Abrahamsson (@erik85). Differential Revision: https://developer.blender.org/D10895