R1:c4399313737b

Respect "disabled" custom field status granted by "subtype" configuration in form validation

Summary:
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.

Test Plan:
- Added a "required" Maniphest custom field "F", then "disabled" it in a subtype "S".
- Created a task of subtype…