Get rid of an additional parent field from ScopeCoroutine

    * Leverage already presented information in our implementation, just expose it via already present internal interface

kotlinx-coroutines-core/api/kotlinx-coroutines-core.api

@@ -86,6 +86,7 @@ public final class kotlinx/coroutines/CancellableContinuationKt {
 
 public abstract interface class kotlinx/coroutines/ChildHandle : kotlinx/coroutines/DisposableHandle {
 	public abstract fun childCancelled (Ljava/lang/Throwable;)Z
+	public abstract fun getParent ()Lkotlinx/coroutines/Job;
 }
 
 public abstract interface class kotlinx/coroutines/ChildJob : kotlinx/coroutines/Job {
@@ -471,6 +472,7 @@ public final class kotlinx/coroutines/NonDisposableHandle : kotlinx/coroutines/C
 	public static final field INSTANCE Lkotlinx/coroutines/NonDisposableHandle;
 	public fun childCancelled (Ljava/lang/Throwable;)Z
 	public fun dispose ()V
+	public fun getParent ()Lkotlinx/coroutines/Job;
 	public fun toString ()Ljava/lang/String;
 }
 

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

@@ -466,6 +466,14 @@ public interface ParentJob : Job {
 @InternalCoroutinesApi
 @Deprecated(level = DeprecationLevel.ERROR, message = "This is internal API and may be removed in the future releases")
 public interface ChildHandle : DisposableHandle {
+
+    /**
+     * Returns the parent of the current parent-child relationship.
+     * @suppress **This is unstable API and it is subject to change.**
+     */
+    @InternalCoroutinesApi
+    public val parent: Job?
+
     /**
      * Child is cancelling its parent by invoking this method.
      * This method is invoked by the child twice. The first time child report its root cause as soon as possible,
@@ -659,6 +667,9 @@ private fun Throwable?.orCancellation(job: Job): Throwable = this ?: JobCancella
  */
 @InternalCoroutinesApi
 public object NonDisposableHandle : DisposableHandle, ChildHandle {
+
+    override val parent: Job? get() = null
+
     /**
      * Does not do anything.
      * @suppress

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

@@ -1459,6 +1459,7 @@ private class InvokeOnCancelling(
 internal class ChildHandleNode(
     @JvmField val childJob: ChildJob
 ) : JobCancellingNode(), ChildHandle {
+    override val parent: Job get() = job
     override fun invoke(cause: Throwable?) = childJob.parentCancelled(job)
     override fun childCancelled(cause: Throwable): Boolean = job.childCancelled(cause)
 }

kotlinx-coroutines-core/common/src/internal/Scopes.kt

@@ -21,7 +21,7 @@ internal open class ScopeCoroutine<in T>(
     final override fun getStackTraceElement(): StackTraceElement? = null
 
     final override val isScopedCoroutine: Boolean get() = true
-    internal val parent: Job? = context[Job]
+    internal val parent: Job? get() = parentHandle?.parent
 
     override fun afterCompletion(state: Any?) {
         // Resume in a cancellable way by default when resuming from another context