Make struct types overlap with procedures.

Closes PR11971.

collects/tests/typed-racket/succeed/pr11971.rkt

@@ -0,0 +1,14 @@
+#lang racket/load
+
+(module a racket
+  (provide (struct-out foo))
+  (define-struct foo (proc) #:property prop:procedure (struct-field-index proc)))
+
+(module b typed/racket
+  (require/typed 'a
+                 (struct foo ((proc : (Number Number -> Number)))))
+  (if (procedure? (foo +))
+       #t
+       (error 'wrong-branch))) 
+
+(require 'b)

collects/typed-racket/rep/type-rep.rkt

@@ -328,7 +328,8 @@
                        (and proc (type-rec-id proc))
                        poly?
                        pred-id)]
-  [#:key 'struct])
+  ;; This should eventually be based on understanding of struct properties.
+  [#:key '(struct procedure)])
 
 ;; A structure type descriptor
 ;; s : struct