When formatting special values, we currently have `NameId` doing `if
(*this == SelfValue)`, `BoolValue` doing `case 0:`, and `TypeId` doing
`if (index == TypeType.index)`. I'm suggesting we consolidate onto the
`*this == SelfValue` approach for consistency, it seems the easiest to
see the mapping of values.
This mixes in #3552 because I'm adding `Exports` there. I'm suggesting
reformatting `Empty` and `Exports` consistent with `Unreachable`.