R1:608e1d20b48a

Write separate comments for every action in Audit

Summary:
Ref T4896. Depends on D10023. Prepares the code for the final migration.

The transaction table stores one row per distinct effect (e.g., add CCs) rather than one row per user action (e.g., "add CCs + comment"). We can double-read that table as long as the code doesn't expect transactions/comments to have multiple different effects, and doesn't try to write any such rows.

Everywhere that we were writing a big "X + Y" comment, write two separate…