compile WebAssembly in CI

[tombl]

The current wasm build is broken because it's untested in CI. This PR fixes the issue and adds a wasm build.

(I can back out any changes if unwanted, but I'm hoping to follow up this PR with one to automate releases and add npm publishing.)

[tombl]

although now that I look at it, build_wasm.ts probably needs resyncing with https://github.com/nodejs/undici/blob/main/build/wasm.js.

[ShogunPanda]

@tombl In general it looks good me. The only thing I don't like is having bash scripts, which are harder to debug.
Can you please sync the undici build script with build_wasm.ts? (if you feel more comfortable, you can also change it to be build_wasm.js).

[Angelmmiguel]

Hey! I've just found this PR after facing the #559 issue. Is this still WIP? I'm happy to jump in and try to solve what's missing here.

Thanks!

[tombl]

Thanks for the reminder on this PR, just copied over undici's build script and tweaked it to fit. Should be all good now?

[ShogunPanda]

Hello!
To be honest I would prefer not to change anything else than the changes in the workflow file. Can you please restore Dockerfile and similar so that the workflow uses the original script?

[ShogunPanda]

Hi again!
@tombl Thanks for your contribution, I've included it in #567, where I also refactored the entire workflow a bit. Closing this.