R1:009aff1a23d8

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