JS: prohibit native (external) extension properties and functions. See KT-13896

js/js.translator/testData/box/expression/function/_common.kt

@@ -1,10 +1,10 @@
 package foo
 
-external fun String.replace(regexp: RegExp, replacement: String): String = noImpl
+inline fun String.replace(regexp: RegExp, replacement: String): String = asDynamic().replace(regexp, replacement)
 
 fun String.replaceAll(regexp: String, replacement: String): String = replace(RegExp(regexp, "g"), replacement)
 
-external fun String.search(regexp: RegExp): Int = noImpl
+inline fun String.search(regexp: RegExp): Int = asDynamic().search(regexp)
 
 external class RegExp(regexp: String, flags: String = "") {
     fun exec(s: String): Array<String>? = noImpl