Review face for export dispatcher highlighted keys

* lisp/org-faces.el (org-dispatcher-highlight): Define new face.

* lisp/ox.el (org-export--dispatch-ui): Apply org-dispatcher-highlight
face.

The intent is to decouple the dispatcher's interface from the generic
org-warning face.  The dispatcher's active keys are thus made easier
to tell apart, without interfering with other applications of
org-warning.

lisp/org-faces.el

@@ -45,6 +45,20 @@ The foreground color of this face should be equal to the background
 color of the frame."
   :group 'org-faces)
 
+(defface org-dispatcher-highlight
+  '((default :weight bold)
+    (((class color) (min-colors 88) (background dark))
+     :background "gray20" :foreground "gold1")
+    (((class color) (min-colors 88) (background light))
+     :background "SlateGray1" :foreground "DarkBlue")
+    (((class color) (min-colors 16) (background dark))
+     :foreground "yellow")
+    (((class color) (min-colors 16) (background light))
+     :foreground "blue")
+    (t :inverse-video t))
+  "Face for highlighted keys in the dispatcher."
+  :group 'org-faces)
+
 (defface org-level-1 '((t :inherit outline-1))
   "Face used for level 1 headlines."
   :group 'org-faces)

lisp/ox.el

@@ -6706,7 +6706,7 @@ back to standard interface."
 	    ;; on the first key, if any.  A nil value means KEY will
 	    ;; only be activated at first level.
 	    (if (or (eq access-key t) (eq access-key first-key))
-		(propertize key 'face 'org-warning)
+		(propertize key 'face 'org-dispatcher-highlight)
 	      key)))
 	 (fontify-value
 	  (lambda (value)