Introduce redundant enum CoroutineSingletons in experimental.intrinsics

libraries/stdlib/jvm/src/kotlin/coroutines/experimental/intrinsics/IntrinsicsJvm.kt

@@ -115,6 +115,11 @@ private inline fun <T> buildContinuationByInvokeCall(
  * the execution was suspended and will not return any result immediately.
  */
 @SinceKotlin("1.1")
-public actual val COROUTINE_SUSPENDED: Any get() = CoroutineSuspendedMarker
+public actual val COROUTINE_SUSPENDED: Any get() = CoroutineSingletons.COROUTINE_SUSPENDED
 
-private object CoroutineSuspendedMarker
+// Using enum here ensures two important properties:
+//  1. It makes SafeContinuation serializable with all kinds of serialization frameworks (since all of them natively support enums)
+//  2. It improves debugging experience, since you clearly see toString() value of those objects and what package they come from
+private enum class CoroutineSingletons {
+    COROUTINE_SUSPENDED
+}