Add external editor mappings to Command Line and Text Edit modes.

This is bound to <C-i> in each of these modes as it is for Insert mode.

--HG--
extra : rebase_source : 846abe669c943637de39a8def11e30d812f01fc2

common/content/editor.js

@@ -570,7 +570,8 @@ const Editor = Module("editor", {
             ["<S-Insert>"], "Insert clipboard/selection",
             function () { editor.pasteClipboard(); });
 
-        mappings.add(modes.getCharModes("i"),
+        // TODO: a better way to specify mode types
+        mappings.add(modes.getCharModes("i").concat(modes.TEXT_EDIT, modes.COMMAND_LINE),
             ["<C-i>"], "Edit text field with an external editor",
             function () { editor.editFieldExternally(); });