Translate backslash-saturated regexp to rx

* lisp/minibuffer.el (minibuffer--regexp-propertize):
The original regexp had 83 backslashes in 147 characters which may be
some kind of record.  This transformation cuts it down to 6, and the
generated regexp string is about 14 % shorter.

lisp/minibuffer.el

@@ -4676,8 +4676,14 @@ and `blink-matching-paren' more user-friendly."
         (remove-text-properties (point-min) (point-max) '(syntax-table nil))
         (goto-char (point-min))
         (while (re-search-forward
-                "\\(\\\\\\\\\\)\\|\\(?:\\(?:\\\\\\)\\(?:\\([(){}]\\)\\|\\(\\[\\)\\|\\(\\]\\)\\)\\)\
-\\|\\(\\[:[a-zA-Z]+:\\]\\)\\|\\(\\[\\)\\|\\(\\]\\)\\|\\([(){}]\\)"
+                (rx (| (group "\\\\")
+                       (: "\\" (| (group (in "(){}"))
+                                  (group "[")
+                                  (group "]")))
+                       (group "[:" (+ (in "A-Za-z")) ":]")
+                       (group "[")
+                       (group "]")
+                       (group (in "(){}"))))
 	        (point-max) 'noerror)
 	  (cond
            ((match-beginning 1))                ; \\, skip