Return task descriptions from "maniphest.search"

Summary:
Fixes T12461. This returns the field as a dictionary with a `"raw"` value, so we could eventually do this if we want without breaking the API:

```
{
  "type": "remarkup",
  "raw": "**raw**",
  "html": "<strong>raw</strong>",
  "text": "raw"
}
```

Test Plan: Called `maniphest.search`, reviewed output.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T12461

Differential Revision: https://secure.phabricator.com/D17603

src/applications/maniphest/storage/ManiphestTask.php

@@ -473,6 +473,10 @@ final class ManiphestTask extends ManiphestDAO
         ->setKey('title')
         ->setType('string')
         ->setDescription(pht('The title of the task.')),
+      id(new PhabricatorConduitSearchFieldSpecification())
+        ->setKey('description')
+        ->setType('remarkup')
+        ->setDescription(pht('The task description.')),
       id(new PhabricatorConduitSearchFieldSpecification())
         ->setKey('authorPHID')
         ->setType('phid')
@@ -501,7 +505,6 @@ final class ManiphestTask extends ManiphestDAO
   }
 
   public function getFieldValuesForConduit() {
-
     $status_value = $this->getStatus();
     $status_info = array(
       'value' => $status_value,
@@ -519,6 +522,9 @@ final class ManiphestTask extends ManiphestDAO
 
     return array(
       'name' => $this->getTitle(),
+      'description' => array(
+        'raw' => $this->getDescription(),
+      ),
       'authorPHID' => $this->getAuthorPHID(),
       'ownerPHID' => $this->getOwnerPHID(),
       'status' => $status_info,