JS: allow to inherit external classes with overloaded functions in case we don't override them (see KT-13910).

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

@@ -0,0 +1,36 @@
+external open class A {
+    open fun f(x: Int) = "number"
+
+    open fun f(x: String) = "string"
+}
+
+class B : A() {
+    fun g(x: Int) = "[${f(x)}]"
+
+    fun g(x: String) = "[${f(x)}]"
+}
+
+interface I {
+    fun f(x: Int): String
+}
+
+class C : A(), I
+
+external interface J {
+    fun f(x: Int): String
+}
+
+class D : A(), J
+
+fun box(): String {
+    var result = B().g(23) + B().g("foo")
+    if (result != "[number][string]") return "fail1: $result"
+
+    result = C().f(42)
+    if (result != "number") return "fail2: $result"
+
+    result = D().f("bar")
+    if (result != "string") return "fail3: $result"
+
+    return "OK"
+}