Add convenience wrapper for regexp disassembly

* lisp/emacs-lisp/disass.el (re-disassemble): New.
* etc/NEWS: Describe the new function instead of the internal
`re--describe-compiled`.

lisp/emacs-lisp/disass.el

@@ -301,6 +301,23 @@ OBJ should be a call to BYTE-CODE generated by the byte compiler."
 	  (insert "\n")))))
   nil)
 
+(defun re-disassemble (regexp &optional case-table)
+  "Describe the compiled form of REGEXP in a separate window.
+If CASE-TABLE is non-nil, use it as translation table for case-folding.
+
+This function is mainly intended for maintenance of Emacs itself
+and may change at any time.  It requires Emacs to be built with
+`--enable-checking'."
+  (interactive "XRegexp (Lisp expression): ")
+  (let ((desc (with-temp-buffer
+                (when case-table
+                  (set-case-table case-table))
+                (let ((case-fold-search (and case-table t)))
+                  (re--describe-compiled regexp)))))
+    (with-output-to-temp-buffer "*Regexp-disassemble*"
+      (with-current-buffer standard-output
+        (insert desc)))))
+
 (provide 'disass)
 
 ;;; disass.el ends here