Remove requirement that job of the pre-created JobCancelNode have to …

…be equal to outer job

Job is supposed to be "sealed" interface, but we also have non-sealed Deferred that can be successfully implemented via delegation and such delegation may break code (if assertions are enabled!) in a very subtle ways.

This assertion is our internal invariant that we're preserving anyway, so it's worth to lift it to simplify life of our users in the future

Fixes #2423

kotlinx-coroutines-core/common/src/JobSupport.kt

@@ -509,12 +509,12 @@ public open class JobSupport constructor(active: Boolean) : Job, ChildJob, Paren
     }
 
     private fun makeNode(handler: CompletionHandler, onCancelling: Boolean): JobNode<*> {
-        return if (onCancelling)
-            (handler as? JobCancellingNode<*>)?.also { assert { it.job === this } }
-                ?: InvokeOnCancelling(this, handler)
-        else
-            (handler as? JobNode<*>)?.also { assert { it.job === this && it !is JobCancellingNode } }
+        return if (onCancelling) {
+            handler as? JobCancellingNode<*> ?: InvokeOnCancelling(this, handler)
+        } else {
+            (handler as? JobNode<*>)?.also { assert { it !is JobCancellingNode } }
                 ?: InvokeOnCompletion(this, handler)
+        }
     }
 
     private fun addLastAtomic(expect: Any, list: NodeList, node: JobNode<*>) =

kotlinx-coroutines-core/common/test/AwaitTest.kt

@@ -351,4 +351,18 @@ class AwaitTest : TestBase() {
             async(NonCancellable) { throw TestException() }
         joinAll(job, job, job)
     }
+
+    @Test
+    fun testAwaitAllDelegates() = runTest {
+        expect(1)
+        val deferred = CompletableDeferred<String>()
+        val delegate = object : Deferred<String> by deferred {}
+        launch {
+            expect(3)
+            deferred.complete("OK")
+        }
+        expect(2)
+        awaitAll(delegate)
+        finish(4)
+    }
 }