Provide high-performance and reusable CancellableContinuation implementation

[elizarov]

Consider the following code that reads some bytes in a loop:

suspend fun foo() {
   while (true) {
       val bytes = readBytes(buf) // suspending
       if (bytes < 0) break
   }
}

where readBytes is written via suspendCancellableCoroutine. The problem is that each readBytes invocation allocates a new CancellableContinuationImpl object and some auxiliary ones to track parent's cancellation. This is unacceptable for high-performance IO code and a standard solution need to be provided for that. For 1.0 release we are looking for an experimental implementation of such an API that relies on new feature in 1.3 coroutines: ContinuationInterceptor.releaseInterceptedContinuation.

[qwwdfsad]

Will be fixed in 1.3.3 by #1534