Measuring test coverage from compiled wasm

[gilengel]

Is your feature request related to a problem? Please describe.
Automatically testing with coverage Chama is currently only possible for unit tests that are compiled with x86-x64 toolchain. The default toolchain /target of Chama is WASM for which unfortunately coverage instructions are not available (missing support in wasm-bindgen).

Describe the solution you'd like
Having coverage information available with the normal toolset without any special configuration. It should work out of the box just call
wasm-pack test

Describe alternatives you've considered
There is not really an alternative. We could ignore the coverage for browser tests but this minimize the chance for us to convince potential developers of the quality of Chama.

Additional context
https://motley-coder.com/2019/03/31/webassembly-coverage/
https://github.com/Amanieu/minicov

rustwasm/wasm-bindgen#2276