Allow EditEngine form fields to be locked and hidden

Summary:
Ref T9132. Allows fields to be locked (shown, but not modifiable) and hidden (not shown).

In both cases, default values are still respected.

This lets you do things like create a form that generates objects with specific projects, policies, etc.

Test Plan:

• Set defaults.
• Locked and hid a bunch of fields.
• Created new objects using the resulting form.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T9132

Differential Revision: https://secure.phabricator.com/D14509