R1:6bdd74584ef3

Fix file encoding migration

Summary:
See [[ https://discourse.phabricator-community.org/t/file-encryption-corruption-when-trying-to-encode-existing-files/1605 | Discourse ]]

When migrating to aes-256-cbc, integrity hashes were not updated, so data was not properly

Test Plan:
I ran [[ https://gist.github.com/kaendfinger/3e0d78350af0ebe4e74b2c8a79707bae | this test script ]] to ensure it worked.
I created some files with lipsum, ensured that after encoding them with aes-256-cbc, they were not able to be…