This commit updates the `walrus` crate used in `wasm-bindgen`. The major
change here is how `walrus` handles element segments, exposing segments
rather than trying to keep a contiugous array of all the elements and
doing the splitting itself. That means that we need to do mroe logic
here in `wasm-bindgen` to juggle indices, segments, etc.
This commit is a pretty large scale rewrite of the internals of wasm-bindgen. No user-facing changes are expected as a result of this PR, but due to the scale of changes here it's likely inevitable that at least something will break. I'm hoping to get more testing in though before landing!
The purpose of this PR is to update wasm-bindgen to the current state of the interface types proposal. The wasm-bindgen tool was last updated when it was still called "WebIDL bindings" so it's been awhile! All support is now based on https://github.com/bytecodealliance/wasm-interface-types which defines parsers/binary format/writers/etc for wasm-interface types.
This is a pretty massive PR and unfortunately can't really be split up any more afaik. I don't really expect realistic review of all the code here (or commits), but some high-level changes are:
* Interface types now consists of a set of "adapter functions". The IR in wasm-bindgen is modeled the same way not.
* Each adapter function has a list of instructions, and these instructions work at a higher level than wasm itself, for example with strings.
* The wasm-bindgen tool has a suite of instructions which are specific to it and not present in the standard. (like before with webidl bindings)
* The anyref/multi-value transformations are now greatly simplified. They're simply "optimization passes" over adapter functions, removing instructions that are otherwise present. This way we don't have to juggle so much all over the place, and instructions always have the same meaning.
This commit switches all of `wasm-bindgen` from the `failure` crate to
`anyhow`. The `anyhow` crate should serve all the purposes that we
previously used `failure` for but has a few advantages:
* It's based on the standard `Error` trait rather than a custom `Fail`
trait, improving ecosystem compatibility.
* We don't need a `#[derive(Fail)]`, which means that's less code to
compile for `wasm-bindgen`. This notably helps the compile time of
`web-sys` itself.
* Using `Result<()>` in `fn main` with `anyhow::Error` produces
human-readable output, so we can use that natively.
This tiny crate provides utilities for working with Wasm codegen
conventions (typically established by LLVM or lld) such as getting the shadow
stack pointer.
It also de-duplicates all the places in the codebase where we were implementing
these conventions in one-off ways.
