Support for having an input and output socket in the same socket declaration
builder was added for the original node panels to be able to support inline
sockets. However, those were generally disabled for now. As can be seen in the
simulation and repeat zone, inline sockets can work differently too. Having an
input and output in the same socket declaration builder builder makes some
things simpler but makes other things much harder. For example, the current
design wouldn't work all that well if the input and output socket has different
types. This is easier to do with the `align_with_previous_socket` approach.
I'm not yet entirely sure whether we want to use the same approach for
corresponding sockets in the node tree interface, but that can be tried and
decided separately.
Pull Request: https://projects.blender.org/blender/blender/pulls/119599
42093bbe3d