iter 22b.2.1: add Constraint struct, Type::Forall.constraints

crates/ailang-surface/src/parse.rs

@@ -858,6 +858,7 @@ impl<'a> Parser<'a> {
         self.expect_rparen("forall-type")?;
         Ok(Type::Forall {
             vars,
+            constraints: vec![],
             body: Box::new(body),
         })
     }