sql: lookup user info using stable ids

Now that we've added ids to users in #81457

Once the remaining migrations are completed #87079
We can update all current lookups that depend on usernames (ie CheckPrivilegeForUser) to use IDs instead.
To do this, we'll need to lookup every usage of SQLUsername and audit if it should use id for lookup.

This PR can be worked on but will likely be hard to rebase.
#79965