R1:3ef270b2926e

Allow transaction publishers to pass binary data to workers

Summary:
Ref T8672. Ref T9187. Root issue in at least one case is:

- User makes a commit including a file with some non-UTF8 text (say, a Japanese file full of Shift-JIS).
- We pass the file to the TransactionEditor so it can inline or attach the patch if the server is configured for these things.
- When inlining patches, we convert them to UTF8 before inlining. We must do this since the rest of the mail is UTF8.
- When attaching…