Light Wallet: Implement mithril-client WASM library

[jpraynaud]

Why

Following the release of the mithril-client library in #1311, we want to extend the availability of the library to WASM binaries.

ℹ We have already created a prototype implementation of the WASM version of the library in the issue #1284

What

Build the mithril-client and mithril-common libraries in WASM.
Run the built mithril-client library in the browser and make it verify a certificate chain.

Definition of Done

The mithril-client library should be partially WASM compatible, published on npm registry and well documented.

How

• Build the WASM package:
  • Adapt the mithril-client library (and mithril-common) to compile as a WASM package
  • Implement mithril-client-wasm crate which exposes a JavaScript API
• Deployment of the WASM package:
  • Optimize the build size of the WASM library (see Build)
  • Run WASM tests in the CI (see Testing your project and Writing Asynchronous Tests)
  • Add packaging in the CI/CD (see Package Code for npm)
  • Add package README
  • Add documentation for mithril-client-wasm package (with browser requirements WASM + BroadcastChannel)
  • Add example(s) for JavaScript usage
• To do also:
  • Add entry for mithril-client-wasm crate in repository README
  • Synchronize secrets in GitHub
  • Synchronize secrets in Vault

Later

• Make a fake aggregator standalone binary (independent issue)
• Implement mithril-client-wasm tests (Firefox/Chrome/Node) with the fake aggregator
• Add WASM client step in Mithril Client multi-platform test
• Implement the mithril client WASM package in the Mithril explorer (certificate chain verification)
• Implement a manual workflow to publish to npm

Parent issue

#1313