fix(serde): Rename visit_struct_key to visit_struct_field

This is more consistent with the rest of the serde naming patterns.

serde_codegen/src/de.rs

@@ -917,7 +917,7 @@ fn deserialize_field_visitor(
                     }
                 }
 
-                deserializer.visit_struct_key(__FieldVisitor::<D>{ phantom: PhantomData })
+                deserializer.visit_struct_field(__FieldVisitor::<D>{ phantom: PhantomData })
             }
         }
     ).unwrap();