JS: Make js Error to be mapped to kotlin.Throwable, inherit Exception and Error from Throwable.

js/js.libraries/src/core/javalang.kt

@@ -1,5 +1,8 @@
 package java.lang
 
+library
+open public class Error(message: String? = null): Throwable(message) {}
+
 library
 open public class Exception(message: String? = null): Throwable(message) {}