Introduce CancellationException

#KT-39126 Fixed

libraries/stdlib/js/src/kotlin/coroutines/cancellation/CancellationException.kt

@@ -0,0 +1,15 @@
+/*
+ * Copyright 2010-2020 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
+ */
+
+package kotlin.coroutines.cancellation
+
+@ExperimentalStdlibApi
+@SinceKotlin("1.4")
+public actual open class CancellationException : IllegalStateException {
+    actual constructor() : super()
+    actual constructor(message: String?) : super(message)
+    constructor(message: String?, cause: Throwable?) : super(message, cause)
+    constructor(cause: Throwable?) : super(cause)
+}