Improve textsec-domain-suspicious-p message

* lisp/international/textsec.el (textsec-domain-suspicious-p):
Ensure that we're not confusing the user if there's a directional
override in the string we're checking.

lisp/international/textsec.el

@@ -244,8 +244,11 @@ or use certain other unusual mixtures of characters."
     (seq-do
      (lambda (char)
        (when (eq (elt idna-mapping-table char) t)
-         (throw 'found (format "Disallowed character: `%s' (#x%x)"
-                               (string char) char))))
+         (throw 'found
+                (format "Disallowed character: `%s' (#x%x, %s)"
+                        (bidi-string-strip-control-characters (string char))
+                        char
+                        (get-char-code-property char 'name)))))
      domain)
     ;; Does IDNA allow it?
     (unless (puny-highly-restrictive-domain-p domain)

test/lisp/international/textsec-tests.el

@@ -162,6 +162,10 @@
    (textsec-email-address-header-suspicious-p
     "Lars Ingebrigtsen <larsi@gn\N{LEFT-TO-RIGHT ISOLATE}us.org>"))
 
+  (should
+   (textsec-email-address-header-suspicious-p
+    "Lars Ingebrigtsen <larsi@\N{RIGHT-TO-LEFT OVERRIDE}gnus.org>"))
+
   (should (textsec-email-address-header-suspicious-p
            "דגבא <foo@bar.com>")))