Blender Git Loki

Geometry Nodes: use density attribute name instead of index as node input

This implements a workaround for the issue that (for historical reasons)
the names of vertex groups are stored on the object while the actual vertex
group data is stored on the mesh.

The solution is to copy the vertex group names from the object into
the `MeshComponent` so that the information is not lost, when the
object cannot be accessed.