urls: add key binding that toggles whether URLs are displayed on jump-label

By default, the URL isn’t shown on the jump-label. For auto-detect
URLs, doing so is virtually always useless, as the URL is already
visible in the grid.

For OSC-8 URLs however, the URL is often _not_ visible in the
grid. Many times, seeing the URL is still not needed (if you’re doing
‘ls --hyperlink’, you already know what the URIs are).

But it is still useful to have a way to show the URLs.

This patch adds a new key binding action that can be used in url-mode
to toggle the URL on and off in the jump label.

It is bound to ctrl+t by default.

wayland.h

@@ -82,6 +82,7 @@ enum bind_action_search {
 enum bind_action_url {
     BIND_ACTION_URL_NONE,
     BIND_ACTION_URL_CANCEL,
+    BIND_ACTION_URL_TOGGLE_URL_ON_JUMP_LABEL,
     BIND_ACTION_URL_COUNT,
 };