Improve support for interface types
This MR does 3 things:
-
Add
g_type_interface_instantiable_prerequisite()
API -
Use that API to allow interface return types in the FFI marshaller for closures (and thereby in signals)
-
Make g_value_copy() from/to object types to/from interface types work the same way it works between object types.
The commit messages have longer explanations about why I added them, but it comes down to me discovering these issues while working on my GTK4 listview branch.