Blender Git Loki

Geometry Nodes: support outputting collection children as instances

This adds two new input sockets to the Collection Info node:
* `Separate Children`: When turned off, the entire collection is output as a single
collection instance (same behavior as before). When turned on, each child of
the collection is output as a separate instance (children can be objects and collections).
Toggling this input should not change the visual transforms of the output geometry.
* `Reset Children`: Only used when `Separate Children` is on. When used, the transforms
of the instances are reset to the origin. This is useful when one wants to e.g. instance
the collection children separately in the upcoming instancing node.

Part of D12478.