R1:2f8e409876e6

Allow EditEngine forms to be marked as "edit" forms

Summary:
Ref T9132. Ref T9908. This attempts to move us forward on answering this question:

> Which form gets used when a user clicks "Edit Task"?

One answer is "the same form that was used to create the task". There are several problems with that:

- The form might not exist anymore.
- The user might not have permission to see it.
- Some of the fields might be hidden, essentially preventing them from being edited.
- We have to store the value…