`single-clause-match-to-match-define` rule buggy with shadowing

[jackfirth]

As seen in racket/typed-racket#1458, the single-clause-match-to-match-define rule refactors this code:

(define (f x)
  (match x
    [(list x) x]))

Into this code:

(define (f x)
  (match-define (list x) x)
  x)

But this change is broken. In the new code, the x on the right-hand-side of the match-define expression is bound to the x in the (list x) pattern. This is because match-define has binding semantics similar to define, while match is closer to let. I'll have to add a check to that rule to ensure this case doesn't get rewritten.