Blender Git Loki

Cleanup: extract versioning code for remapping node socket animation

When node input sockets are animated, they target the socket by index.
As a result, animation data needs to be updated whenever new sockets are
added (except when they're added at the end of the list). The code for
this is now extracted into its own versioning function, so that it can
be used for other versioning steps as well.

No functional changes.