@sunfishcode added `wasm32-wasi` support in #477, but somewhere along the way it appears to have
been broken or dropped. Thankfully, the reason for the breakage doesn't appear too deep: the
`wasm-bindgen` support was enabled for all `wasm32` architectures, rather than just the
`wasm32-unknown-unknown` target triple that [`wasm-bindgen`
supports](https://rustwasm.github.io/wasm-bindgen/reference/rust-targets.html).

This PR fixes the `cfg` expressions for `wasm-bindgen`-specific code so that they no longer catch
`wasm32-wasi`, and now `wasm32-wasi` just works 🎉

To guard against future breakage, I added some `wasm32-wasi` testing infrastructure. A new CI
target modeled on the `wasm-bindgen` target tests the `wasm32-wasi` implementation against
`wasmtime`. Since test runners can't be specified at the command line, this requires a
`.cargo/config` addition as well.

I also noticed and fixed a typo in the existing `wasm-bindgen` CI target that I believe has been
causing the tests to not run with any of the version features enabled.

Add `wasm32-wasi` support with tests

Fix up MSRV build in CI

fix: keep the order when filling random bytes

Prepare for 1.3.4 release