move the ╬ char and friends into a separate file

do not merge to 5.3.2

original commit: 1edec6a33ed3a98b95a233f6be90d40fd8e1dfc0

collects/framework/private/dir-chars.rkt

@@ -0,0 +1,39 @@
+#lang racket/base
+(require racket/list)
+(provide adjustable-chars
+         up-chars
+         dn-chars
+         lt-chars
+         rt-chars)
+
+(define up-chars
+  '(#\╬ 
+    #\╩ #\╣ #\╠
+    #\╝ #\╚
+    #\║
+    #\+ #\|))
+
+(define dn-chars
+  '(#\╬ 
+    #\╦ #\╣ #\╠
+    #\╗ #\╔
+    #\║
+    #\+ #\|))
+
+(define lt-chars
+  '(#\╬ 
+    #\╩ #\╦ #\╣
+    #\╝ #\╗ 
+    #\═ 
+    #\+ #\-))
+
+(define rt-chars
+  '(#\╬ 
+    #\╩ #\╦ #\╠
+    #\╔ #\╚
+    #\═
+    #\+ #\-))
+
+(define adjustable-chars
+  (remove-duplicates
+   (append up-chars dn-chars lt-chars rt-chars)))