what you get if you use recursive newtypes. (They are rare, so who
cares if they are a tiny bit less efficient.)
+So: non-recursive newtypes are represented using a SourceTy (see below)
+ recursive newtypes are represented using a TyConApp
+
The TyCon still says "I'm a newtype", but we do not represent the
newtype application as a SourceType; instead as a TyConApp.