Add kotlin.coroutines.cancellation.CancellationException to stdlib

runtime/src/main/kotlin/kotlin/coroutines/CancellationException.kt

@@ -0,0 +1,18 @@
+/*
+ * Copyright 2010-2020 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license
+ * that can be found in the LICENSE file.
+ */
+
+package kotlin.coroutines.cancellation
+
+/**
+ * Thrown by cancellable suspending functions if the coroutine is cancelled while it is suspended.
+ * It indicates _normal_ cancellation of a coroutine.
+ */
+@SinceKotlin("1.4")
+public open class CancellationException : IllegalStateException {
+    constructor() : super()
+    constructor(message: String?) : super(message)
+    constructor(message: String?, cause: Throwable?) : super(message, cause)
+    constructor(cause: Throwable?) : super(cause)
+}