JS: report errors on different external items:

* data classes
* val/var parameters of primary constructors
* enum entry with body
* anonymous `init {}` block in classes

js/js.translator/testData/box/native/classObject.kt

@@ -1,6 +1,8 @@
 package foo
 
-external class A(val c: Int) {
+external class A(c: Int) {
+    val c: Int
+
     companion object {
         val g: Int
         val c: String = noImpl