Functions: add debug utility for lazy function graphs

This makes it easier to print information about a socket. Just the
socket name is sometimes not enough information to know where
it is in the graph.

source/blender/functions/FN_lazy_function_graph.hh

@@ -78,6 +78,7 @@ class Socket : NonCopyable, NonMovable {
   const CPPType &type() const;
 
   std::string name() const;
+  std::string detailed_name() const;
 };
 
 class InputSocket : public Socket {