This adds support for specifying structure types on closures. The main immediate
benefit is that this makes it possible to use fields with closures (without
having incorrect warnings in the UI).
A closure zone behaves very similar to a node group with respect to structure
type inferencing. The structure types can be inferenced fully automatically, or
the user can specify them manually on the closure inputs. On the evaluate
closure zone, the user has to specify the structure types of the inputs and
outputs explicitly (or leave them as dynamic).
Working on this, I was a bit surprised that `get_output_socket_shape` depended
on the field state. Is that a left-over? It feels like it shouldn't be necessary
since the socket shape shouldn't depend on field inferencing anymore. I removed
that now and couldn't see a difference yet.
The operator that creates a closure zone from an evaluate closure node copies
the input structure types already. Beyond that, there is no automatic syncing of
the structure types yet. The structure types only affect the UI and not what's
actually done during evaluation.
Pull Request: https://projects.blender.org/blender/blender/pulls/139713
152471ffdb