Provide contextual documentation explaining how to prefill ApplicationEditor create forms

Summary:
Ref T9132. Although forms do generally support prefilling right now, you have to guess how to do it.

Provide an explicit action showing you which values are supported and how to prefill them. This is generated automatically when an application switches to ApplicationEditor.

Test Plan:
{F939804}

{F939805}

{F939806}

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T9132

Differential Revision: https://secure.phabricator.com/D14392