This patch allows connecting wires for object and collection socket
types to the "Group Input" node, which exposes them to be adjusted
in the modifier.
Thanks a lot to @angavrilov for working on this. I was working on this
as well, but Alexander fixed a few more issues than I did, so his version
is here with some edits.
The patch is composed of a few different changes:
- Add code to create pointer properties in the modifier settings for
object and collection sockets, and also to draw them in the UI.
- Also search through the modifier's `IDProperty` settings to find IDs
used by the modifier.
- A bug fix in RNA_acces.c for setting pointer `IDProperty` values.
- Make pointer `IDProperty` values editable. Previously there was just
no need for this.