Add positional_count field to Lambda

This field is used for static optimization, determining if parameters
are purely positional.

src/ast/compiler/dumper.rs

@@ -117,7 +117,7 @@ impl Dumper {
                 self.indent -= 1;
             }
 
-            BoundKind::Lambda { params, upvalues, body } => {
+            BoundKind::Lambda { params, upvalues, body, .. } => {
                 self.log(&format!("Lambda (Upvalues: {})", upvalues.len()), node);
                 self.indent += 1;