R1:a31a7809b02e

Fix a type issue with FormView juggling

Summary:
When you click the pencil icon in the Maniphest task list, we currently fatal:

Argument 1 passed to PhabricatorCustomFieldList::appendFieldsToForm() must be an instance of AphrontFormView, instance of PHUIFormLayoutView given, called in /core/lib/phabricator/src/applications/maniphest/controller/ManiphestTaskEditController.php on line 576 and defined

This is because we build an `AphrontFormView` noramlly, but a `PHUIFormLayoutView` for dialogs, since…