Rust: Handle ref patterns in data flow

To do this we:
* Let SSA writes target the name inside identifier patterns instead of
  the pattern itself
* Include relevant names in the data flow graph
* Add a store step from a identifier patterns with `ref` into the
  contained name. So we have an edge `ref a` -> `a` that stores in the
  reference content type.

rust/schema/annotations.py

@@ -1336,7 +1336,7 @@ class _:
     """
 
 
-@annotate(Name)
+@annotate(Name, cfg=True)
 class _:
     """
     A Name. For example: