Ref T12314. When we pick an "Edit" form for a subtyped object, only consider forms with the same subtype.

For example, editing an "Animal" uses the forms with subtype "animal" which are marked as edit forms.

This also makes "Create Subtask" carry the parent task's type.

• Edited an Animal, got an animal edit form.
• Edited a normal task, got a normal task form.
• Edited a paste, got the normal workflow.