R1:df0f5c6cee03

Make repository identity email address association case-insensitive

Summary:
Ref T13444. Currently, identities for a particular email address are queried with "LIKE" against a binary column, which makes the query case-sensitive.

- Extract the email address into a separate "sort255" column.
- Add a key for it.
- Make the query a standard "IN (%Ls)" query.
- Deal with weird cases where an email address is 10000 bytes long or full of binary junk.

Test Plan:
- Ran migration, inspected database for…