Process Remarkup in text and HTML email bodies appropriately

Summary: Ref T6343, adding HTMLMailMode to remarkup, and most objects should now be processed and appear pretty in emails.

Test Plan: Add a comment to a Maniphest task containing a mention of an object like '{T1}' or 'T1'. Emails should show a styled version of the object similar to how the object looks in the context of the Maniphest task in the UI.

Reviewers: epriestley, #blessed_reviewers

Reviewed By: epriestley, #blessed_reviewers

Subscribers: chad, Korvin, epriestley

Maniphest Tasks: T6343, T2617

Differential Revision: https://secure.phabricator.com/D10859

src/applications/phriction/markup/PhrictionRemarkupRule.php

@@ -29,9 +29,12 @@ final class PhrictionRemarkupRule extends PhutilRemarkupRule {
     $slug     = PhrictionDocument::getSlugURI($slug);
     $href     = (string)id(new PhutilURI($slug))->setFragment($fragment);
 
+    $text_mode = $this->getEngine()->isTextMode();
+    $mail_mode = $this->getEngine()->isHTMLMailMode();
+
     if ($this->getEngine()->getState('toc')) {
       $text = $name;
-    } else if ($this->getEngine()->isTextMode()) {
+    } else if ($text_mode || $mail_mode) {
       return PhabricatorEnv::getProductionURI($href);
     } else {
       $text = $this->newTag(