gtk: fix drag-and-drop URI decoding

Closes PR 11695
 Merge to 5.1

original commit: 2d01241f7ad3c3905a9629c6aa33ad7cd4c7e653

collects/mred/private/wx/gtk/window.rkt

@@ -1,6 +1,7 @@
 #lang racket/base
 (require ffi/unsafe
          racket/class
+	 net/uri-codec
          ffi/unsafe/atomic
          "../../syntax.rkt"
          "../../lock.rkt"
@@ -121,7 +122,10 @@
 	    => (lambda (m)
 		 (queue-window-event wx
 				     (lambda ()
-				       (let ([path (bytes->path (cadr m))])
+				       (let ([path 
+					      (string->path
+					       (uri-decode
+						(bytes->string/utf-8 (cadr m))))])
 					 (send wx on-drop-file path)))))]))))))
 
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