Implement common Throwable.addSuppressed/suppressed extensions

Instead of `suppressed` Array we provide `suppressedExceptions` List

#KT-23737

libraries/stdlib/js/test/core/testUtils.kt

@@ -1,5 +1,5 @@
 /*
- * Copyright 2010-2019 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * 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.
  */
 
@@ -23,4 +23,6 @@ public actual fun testOnJvm(action: () -> Unit) { }
 public actual fun testOnJs(action: () -> Unit) = action()
 
 // TODO: should be true at least in JS IR after implementing KT-24975
-public actual val isFloat32RangeEnforced: Boolean = false
+public actual val isFloat32RangeEnforced: Boolean = false
+
+actual val supportsSuppressedExceptions: Boolean get() = true