This is a fairly verbose part of nodes RNA, which defines the base
NodeSocket and NodeSocketInterface types as well as all the subtypes
required for showing correct properties based on socket type.
The RNA for this part of nodes is quite self-contained, so moving it
to a separate files works well and reduces the overall size of
rna_nodetree.cc considerably (~1700 LoC). This does not include any
functional changes.
Moving this to a separate file will make it easier to improve the node
group interface (#109135).
Pull Request: https://projects.blender.org/blender/blender/pulls/110220
3e3133192a