Attach struct info to constructor for polymorphic TR structs.

Closes PR 12806

collects/tests/typed-racket/succeed/pr12806.rkt

@@ -0,0 +1,12 @@
+#lang racket/load
+
+(module a typed/racket
+  (struct: (V) foo ((v : V)))
+  (provide foo))
+
+(module b racket
+  (require 'a)
+
+  (foo 2))
+
+(require 'b)

collects/typed-racket/typecheck/tc-structs.rkt

@@ -240,6 +240,7 @@
   (mk/register-sty nm flds parent-name parent-field-types types
                    #:maker maker
                    #:mutable mutable
+                   #:struct-info (syntax-property nm/par 'struct-info)
                    ;; wrap everything in the approriate forall
                    #:wrapper (λ (t) (make-Poly tvars t))
                    #:type-wrapper (λ (t) (make-App t new-tvars #f))