setup code coverage for kotlin js

[robstoll]

Platform (all, jvm, js): all
Extension (none, kotlin 1.3): none

Code related feature

So far we only collect code coverage for JVM but not for JS (e.g. turnTestNodesIntoExpectGrouping is not covered due to this fact). It would be nice if we would see additionally what js specific code is actually covered and what not.

TODO:

• [] setup code coverage for js
• [] push it to codecov -- I guess this should work already work as long as the file format is supported by codecov -- happens here .github/workflows/quality-assurance.yml -> Upload build code coverage

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