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

compiler/testData/diagnostics/testsWithJsStdLib/name/overrideOverloadedNativeFunction.kt

@@ -0,0 +1,9 @@
+external open class A {
+    open fun f(x: Int): Unit
+
+    <!JS_NAME_CLASH!>open fun f(x: String): Unit<!>
+}
+
+class InheritClass : A() {
+    <!JS_NAME_CLASH!>override fun f(x: Int): Unit<!> { }
+}