KJS: implement Throwable in Kotlin instead of use it as alias of JS Error

* Make it an inheritor of JS Error. Otherwise, Chakra engine doesn't fill stack trace of exception; In other engines inheritance has some good effects too.
* Copy all properties from internally created instance of JS Error

 #KT-6985 Fixed
 #KT-2328 Fixed
 #KT-8019 Fixed
 #KT-10911 Fixed

js/js.translator/testData/box/expression/try/exceptionToString.kt

@@ -0,0 +1,26 @@
+package foo
+
+class MyException(m: String? = null): Exception(m)
+class MyException2(m: String? = null): Throwable(m)
+
+fun check(e: Throwable, expectedString: String) {
+    try {
+        throw e
+    }
+    catch (e: Throwable) {
+        assertEquals(expectedString, e.toString())
+    }
+}
+
+fun box(): String {
+    check(Throwable(), "Throwable: null")
+    check(Throwable("ccc"), "Throwable: ccc")
+    check(Exception(), "Exception: null")
+    check(Exception("bbb"), "Exception: bbb")
+    check(MyException(), "MyException: null")
+    check(MyException("aaa"), "MyException: aaa")
+    check(MyException2(), "MyException2: null")
+    check(MyException2("aaa"), "MyException2: aaa")
+
+    return "OK"
+}