Run tests in parallel using thread argument

[orchestr7]

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Discussed with @petertrr - we should run tests in parallel. One scope is the test. And plugins can be run one-by-one in the scope of one test

Parallel run of tests should be configured by some option in save.properties.

This task can be solved by multiplatform courutines.

[petertrr]

I believe we will be needing https://github.com/Kotlin/kotlinx.atomicfu to implement this; this library also provides multiplatform atomics, like AtomicInt and AtomicBoolean

[orchestr7]

Interesting issue - guys, @nulls @icemachined @0x6675636b796f75676974687562 you can take it. But if you will take - please remove other assignees.

[petertrr]

Related to this is #331. Now we are using coroutines only in an isolated part of code, but for better support of parallelism we should probably lift coroutines entrypoint higher in the code