Light Wallet: Build mithril-common and mithril-client in WASM PoC

[jpraynaud]

Why

When working on the PoC #1254, we have faced some difficulties implementing the current mithril-common and mithril-client in WASM. This is mostly the case because some crates that we have used are not (currently?) compatible with WASM.

The goal of the PoC #1254 was to make sure that we did not have any blocker with working with the cryptographic libraries in WASM.
In order to do so, we have been recreating from scratch some of the libraries of mithril-common that would not compile properly.

We now need to find a way to build the mithril-client library with the linked mithril-common library in WASM

What

Find a way to 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 (PoC).

How

• Build a mithril-client (with mithril-common) in WASM
• Run a mithril-client in a browser (with e.g. Mithril Stake Distribution type)
• Make sure all binary nodes are working as expected
• Make README to use the PoC
• Answer some questions that will have an impact on the new design of the mithril-client:
  • How can we provide feedback to the browser (events sent)? (See use of JS closures in Rust)
  • How do we compile partial API (e.g. no compilation of snapshot download in WASM)?

Linked issue

#1141

[jpraynaud]

The PoC is available in the branch ensemble/1284/build-mithril-common-and-client-wasm-poc