Js frontend: prohibit default values for functions annotated as nativeIndexer.

compiler/testData/diagnostics/testsWithJsStdLib/native/nativeGetter/onNativeClassMembers.kt

@@ -63,6 +63,9 @@ class C {
     nativeGetter
     fun bar(a: String): <!NATIVE_GETTER_RETURN_TYPE_SHOULD_BE_NULLABLE!>Int<!> = 0
 
+    nativeGetter
+    fun baz(<!NATIVE_INDEXER_CAN_NOT_HAVE_DEFAULT_ARGUMENTS!>a: String = "foo"<!>): Int? = 0
+
     class object {
         <!NATIVE_ANNOTATIONS_ALLOWED_ONLY_ON_MEMBER_OR_EXTENSION_FUN!>nativeGetter
         fun Int.get(a: String): Int?<!> = 1