R1:2b7c0ec92f6c

Destroy file attachments when file is deleted, or object is deleted

Summary:
Adds file attachment deletion logics:

- PhabricatorFile: delete the attachment if file is deleted
- destruction engine extension: delete attachment if object is deleted
- SQL patch: delete existing leftover attachments from deleted files

To apply the cleanup, as usual, run:

./bin/storage upgrade

This cleanup may take some time, proportionally to the size of these tables:

phabricator_file.file
phabricator_file.