Improve hash-table overlap.

Thanks to Alex Knauth for the code and Jordan Johnson for the test case.

typed-racket-lib/typed-racket/types/remove-intersect.rkt

@@ -65,6 +65,9 @@
          [(list-no-order (Value: (? simple-datum?))
                          (or (? Struct?) (? StructTop?) (? Function?)))
           #f]
+         [(list-no-order (Value: (not (? hash?)))
+                         (or (? Hashtable?) (? HashtableTop?)))
+          #f]
          [(list (Struct: n _ flds _ _ _)
                 (Struct: n* _ flds* _ _ _)) 
           #:when (free-identifier=? n n*)

typed-racket-test/succeed/json-hash.rkt

@@ -0,0 +1,4 @@
+#lang typed/racket/base
+(require typed/json)
+(: jsx JSExpr)
+(define jsx #hasheq((a . "val1") (b . "val2") (c . "val3")))