This makes the inner `Object` type generic (but defaulting to the same inner
types as before) so that it can be used as a sum type for various types
where `ObjectKind`-based narrowing is required.
In this case, it's used to narrow `ObjectIndex` alongside the inner
`ObjectKind` so that the two are definitely in sync. This not only results
in cleaner code and a more intuitive API that's approachable to people
less familiar with the system, but it also helps to eliminate logic bugs
that might result form manually narrowing (as was done before this change).
DEV-13708
This was a fairly simple addition, since rate blocks already lower into sum
expressions; these are just non-identified.
This does emphasize that the nir::parse `ele_parse!` abstraction I spent so
much time on ended up not being a perfect fit, as it now has some
boilerplate after it was stripped of much of its capabilities some time ago.
Don't worry, `nir::air` and `asg::graph::xmli` will get cleaned up.
DEV-13708
Mike Gerwitz