Still need to make it so that it maps discriminants to variant indexes.
Maybe instead I can map the variant indexes to discriminants?

Changing a bunch of struct constructors to `from`, no extra destructuring,
getting the type of the discriminant.

Since we're changing a bunch of stuff, necessary to remove some codegen tests
which look for specific things. Also attempting to restart a test which timed out, maybe due to
fastly failing?

Instead of storing an extra array for discriminant values, create an allocation there and store
those in an allocation immediately.

There is a distinction between running this on wasm and i686, even though they should be
identical. This technically is not _incorrect_, it's just an unexpected difference, which is
worth investigating, but not for correctness.