Fix Firefox support

[Twey]

Mozilla have recently changed the behaviour in Firefox of new WebAssembly.Module to forbid compiling from a SharedArrayBuffer.

Wasmer (with the web backend) compiles WebAssembly by passing a view of the underlying memory. In our case, the underlying memory is a SharedArrayBuffer, so compilation now fails on Firefox.

We need to fix it by patching Wasmer to copy the data instead of using a view when the underlying memory is a SharedArrayBuffer, but we are so far behind Wasmer mainstream (2 major versions) that it seems worthwhile to try to upstream our changes and the patch (#4203) then upgrade rather than piling more patches onto our fork.

We don't consider this a blocker for Testnet #3.