WASM targets coverage

[ark0f]

Problem to Solve

We don't have code coverage for WASM targets at the moment because wasm32-unknown-unknown target doesn't have profiler_builtins crate required for coverage instrumentation (I doubt it will do ever)

Possible Solution

Extract profiler_builtins crate from Rust sources, modify it for WASM specifity and then integrate it (sysroot, cargo patch feature, etc)

Notes

https://github.com/Amanieu/minicov is very close to that

cargo patch feature doesn't allow to patch such sysroot crates