The typed function references proposal introduces non-defaultable types such as `(ref $t)`. References that inhabit those types must be initialized, and can't be used in an uninitialized state (like null).

As a result, it's necessary to track local initialization state somehow so that `local.get` can be disallowed on uninitialized references, and have a defined result on initialized locals.

The issue tracking the spec algorithm: https://github.com/WebAssembly/function-references/pull/63

The chosen algorithm for this is "1a" from here: https://github.com/WebAssembly/function-references/issues/44#issuecomment-1136373660 (initialization state is reset after each block)