Geometry Nodes: initial support for volumes

For the most part, this just adds boilerplate code for volume support in geometry nodes:
* Add `VolumeComponent` next to `MeshComponent`, etc.
* Support `VolumeComponent` in depsgraph object iterator.

Furthermore, I added initial volume support in a few nodes:
* The Object Info node outputs an object instance when the input is a volume object
  (that will be the same for mesh objects soonish, to avoid copies).
* Support transforming a `VolumeComponent` in the Transform node.
* Support the `VolumeComponent` in Join Geometry nodes, but only when just one of the
  inputs has a volume component for now.

Right now, there is no way to create a `VolumeComponent`, because the Object Info node
outputs an object instance. The `VolumeComponent` will be necessary for upcoming nodes,
which will generate volumes on the fly.

Viewport selection does not work correctly with `VolumeComponent`s currently. I don't
know why that is. That can be figured out a bit later, once we can actually create
new volumes in geometry nodes.

Ref T84604.

Differential Revision: https://developer.blender.org/D10147

source/blender/blenkernel/intern/volume.cc

@@ -523,6 +523,8 @@ static void volume_copy_data(Main *UNUSED(bmain),
     volume_dst->runtime.grids = OBJECT_GUARDED_NEW(VolumeGridVector, grids_src);
   }
 #endif
+
+  volume_dst->batch_cache = nullptr;
 }
 
 static void volume_free_data(ID *id)