Repair some corner cases in cancellation propagation between coroutines and listenable futures (#2222)

* Repair some corner cases in cancellation propagation between coroutines and listenable futures

Implement bidirectional cancellation for `future` coroutine builder.

This also:

* Refactors JobListenableFuture infrastructure so it can be reused in CoroutineScope.future and Deferred.asListenableFuture;
* Provides more descriptive `toString` implementation for the returned Future;
* Fixes stack traces in thrown exception, so it includes a call to get() that triggered the exception to be thrown;
* Hides ListenableFuture.asDeferred return type, so it can't be cast to CompletableDeferred;
* Adds more tests to cover fixed corner cases;
* Improves documentation;
* Suppresses annoying warnings in tests.

Fixes #1442

Author: vadimsemenov