Show login in the user monogram

This is actually appeared handy after discussion with campbell.

src/applications/people/markup/PhabricatorMentionRemarkupRule.php

@@ -134,12 +134,12 @@ final class PhabricatorMentionRemarkupRule extends PhutilRemarkupRule {
                 font-weight: bold;
                 padding: 0 4px;',
             ),
-            '@'.($user->getRealName() ? $user->getRealName() : $user->getUsername()));
+            '@'.$user->getFullName());
         } else {
           $tag = id(new PHUITagView())
             ->setType(PHUITagView::TYPE_PERSON)
             ->setPHID($user->getPHID())
-            ->setName('@'. ($user->getRealName() ? $user->getRealName() : $user->getUsername()))
+            ->setName('@'.$user->getFullName())
             ->setHref($user_href);
 
           if ($user_has_no_permission) {

src/applications/people/storage/PhabricatorUser.php

@@ -274,10 +274,7 @@ final class PhabricatorUser
   }
 
   public function getMonogram() {
-    if ($this->getRealName())
-      return '@'.$this->getRealName();
-    else
-      return '@'.$this->getUsername();
+    return '@'.$this->getFullname();
   }
 
   public function isLoggedIn() {