Add JS specific proto comparison test

Original commit: 239943867b

jps/jps-plugin/testData/comparison/jsOnly/externals/new.kt

@@ -0,0 +1,15 @@
+package test
+
+external class ExternalClass {
+    fun addedExternalFun()
+    val addedExternalVal: Int
+}
+
+external class ClassBecameExternal
+class ClassBecameNonExternal
+
+external fun addedExternalFun()
+external val addedExternalVal: Int
+
+external fun funBecameExternal()
+fun funBecameNonExternal() {}