Review Board 5 introduced a `LocalSite.ALL` value, which could be used to query state without considering a `LocalSite` value (as opposed to a `None` value for the global site). This was a bit hard to type correctly, and we ran the risk of different blocks of code attempting their own typing. This change introduces an `AnyOrAllLocalSites` type, which supports a `LocalSite` instance, `None`, or `ALL`. To make this work, `ALL` needed to be converted from a singleton object to a value supported in `Literal`. The safest approach was to use an enum (which won't unintentionally cast to a string or integer in a query). So we now have a private enum with only an `ALL` value.