R1:42876de60d28

Generate file attachment transactions for explicit Remarkup attachments on common edit pathways

Summary:
Ref T13603. On common edit pathways, extract explicit file attachments from Remarkup. These pathways are affected:

- Objects that use EditEngine and expose a remarkup area via "RemarkupEditField".
- Objects that use EditEngine to generate a comment area.

This is the vast majority of pathways, but not entirely exhaustive.

Test Plan: Created and commented on a task, explicitly attaching images.