Add ability to create a child scope

[dovchinnikov]

Similar to:

launch { // parent
  launch { // child
    ...
  }
}

Given a parent scope, I'd like to be able to attach a child to it. This child scope has to follow coroutine hierarchy w.r.t. cancellation propagation and parent completion.

class MyComponent(parent: CoroutineScope) {
  
  private val cs = parent.childScope(CoroutineName("MyComponent"))

  // launch coroutines in cs  

  fun shutdown() {
    cs.cancel()
  }
}

[circusmagnus]

See issue #2758 :)

[qwwdfsad]

Closing as duplciate