Respect "disabled" custom field status granted by "subtype" configuration in form validation
Fixes T13384. Currently, the subtype "disabled" configuration is not respected when selecting fields for ROLE_EDIT.
The only meaningful caller for ROLE_EDIT is transaction validation, but transaction validation should respect fields being disabled by subtype configuration.
- Added a "required" Maniphest custom field "F", then "disabled" it in a subtype "S".
- Created a task of subtype "S".
- Before: Form submission fails with error "F is required", even though the field is not actually visible on the form and can not be set.
- After: Form submits cleanly and creates the task.
Maniphest Tasks: T13384
Differential Revision: https://secure.phabricator.com/D20726