JS: report errors on different external items:

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

compiler/testData/diagnostics/testsWithJsStdLib/native/anonymousInitializer.kt

@@ -0,0 +1,5 @@
+external class A {
+    <!EXTERNAL_ANONYMOUS_INITIALIZER!>init {
+        noImpl
+    }<!>
+}