Build NPM package and upload as artifact in GHA

[palas]

Changelog

- description: |
    Added NPM package building to GHA
  type:
  - feature        # introduces a new feature
  projects:
  - cardano-wasm

Context

In order to make the publishing of the cardano-wasm package more deterministic, this change allows GHA to build a .tgz file that is ready for publishing.

How to trust this PR

The generated .tgz can be found in the CI run.

Checklist

• Commit sequence broadly makes sense and commits have useful messages
• New tests are added if needed and existing tests are updated. See Running tests for more details
• Self-reviewed the diff

[carbolymer]

Haven't tested it, but it looks fine.

[carbolymer]

This is running in nix anyway, I'm wondering if we could provide dependencies from nix instead. I'm not too familiar with building using npm in nix, so I'm not 100% if that's possible.

[palas]

The js proto bundle is being built with nix, and I think it probably is deterministical, but the actual cardano-wasm JavaScript package is not being built with nix. Maybe it should, good point.

I am not sure what the options for doing it with nix and their consequences are either. I did something like that for the generation of JS files from proto files (here) but, I basically provided a package-lock.json file and it hashes it, I think. On the other hand, package-lock.json file already has hashes for all dependencies. Even though I didn't commit that file to the repo either. Not sure