In future use cases, a volume can contain many grids that represent the
density information. In this case, it's better if the volume to mesh node
creates a mesh based on all of the grids in the volume.
This is also a benefit to share-ability, since one doesn't have to
specify the grid name in the node. Instead, in the future we can have
a way to split particular grids into separate volumes, if only one
grid should be considered.
The code changes are relatively simple:
- Run the volume to mesh node on all instance geometry, like elsewhere
- Make the blenkernel's volume to mesh API a bit more specific
This patch also includes a change to the join geometry node to include
all grids in the output. That won't be committed with this patch, but
it's essential for testing. I'll submit that change separately for 3.1.
