Add "idea://" to the upstream editor whitelist

Summary: This supports the IntelliJ IDEA editor.

Test Plan:
  - Looked at the editor settings panel, saw "idea://".
  - Set my editor pattern to "idea://a?b".
  - (Did not actually install IntelliJ IDEA.)

Differential Revision: https://secure.phabricator.com/D21206

src/applications/config/option/PhabricatorSecurityConfigOptions.php

@@ -213,6 +213,9 @@ EOTEXT
 
           // This handler is for Visual Studio Code.
           'vscode' => true,
+
+          // This is for IntelliJ IDEA.
+          'idea' => true,
         ))
         ->setSummary(pht('Whitelists editor protocols for "Open in Editor".'))
         ->setDescription(

src/applications/settings/panel/PhabricatorExternalEditorSettingsPanel.php

@@ -105,6 +105,7 @@ final class PhabricatorExternalEditorSettingsPanel
       'emacs' => pht('Emacs'),
       'vscode' => pht('Visual Studio Code'),
       'editor' => pht('Generic Editor'),
+      'idea' => pht('IntelliJ IDEA'),
     );
 
     $default_label = phutil_tag('em', array(), pht('Supported Protocol'));