Wasm target implementation

[igoriakovlev]

This is Kotlin/Wasm/JS target implementation for kotlinx.corourines. Mostly this is a port of Kotlin/JS implementation with wasm-related changes, like Kotlin <-> JS interop.

There is dependency to intermediate version to AtomicFU which is not published yet officially into repository. This is why we need atomicFU bootstrap version 0.21.0-wasm0 in wasm experimental repo.

There a lit of similar code with JS and Native implementations. I have tried my best to combine this code into separate shared directory, but there is some number of copy-pasted code for now which is similar but not the same. I look forward to hear possible solutions to avoid this.

Dokka documentation apparently generates links that point to a branch different from master, because adding similar, but not equal declarations for several targets makes different links, which is not exists in current master.

[qwwdfsad]

Please provide a detailed description of the PR as one would do for other Kotlin subsystems:

• Briefly explain what exactly is done in the scope of the PR
  • Including new targets, publication structure and what is left to do
• If the code has any explicit or implicit TODOs or leftovers, please spell them out
• If the PR contains any non-trivial parts that are hard to understand without diving too deep -- please explain them
  • Example 1: PR is red on the CI, cannot be built or imported. Nothing in the PR indicates why so and when should we proceed
  • Example 2: PR has some number of copy-pasted code (which is twice the maintenance and divergence bugs) but no explanation why so and whether there is anything that prevents us from avoiding doing so
  • Example 3: there are innocuously-looking tests that are ignored without any explanation
  • Example 4: Dokka documentation apparently generates links that point to a branch different from master?

[qwwdfsad]

Almost there.

There are a few comments left, and I believe that's it.
Then I'll tweak stuff here and there (mostly our specific documentation and build scripts) and will merge it the moment atomicfu is released

[qwwdfsad]

Thanks, tremendous job