Implement common Throwable.addSuppressed/suppressed extensions

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

#KT-23737

libraries/stdlib/jvm/test/testUtilsJVM.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.
  */
 
@@ -32,4 +32,6 @@ public actual fun testOnJs(action: () -> Unit) {}
 @Suppress("HasPlatformType", "UNCHECKED_CAST")
 public fun <T> platformNull() = Collections.singletonList(null as T).first()
 
-public actual val isFloat32RangeEnforced: Boolean = true
+public actual val isFloat32RangeEnforced: Boolean = true
+
+public actual val supportsSuppressedExceptions: Boolean get() = !isJava6