Connecting to some sockets of a few nodes via the drag link search
would fail and trigger an assert, because the picked socket wasn't
available. This was due to some sockets only being available with
certain settings.
This patch fixes these cases by adding the availability conditions of
the socket to the node declaration with the `make_available` method
or manually adding a `node_link_gather_search` function.
Differential Revision: https://developer.blender.org/D14283
7de3caa05d